feat: implement TelegramClient core module (issue #31)

Add TelegramClient for real-time trading notifications:
- NotificationPriority enum (LOW/MEDIUM/HIGH/CRITICAL)
- LeakyBucket rate limiter (1 msg/sec)
- 8 notification methods (trade, circuit breaker, fat finger, market open/close, system start/shutdown, errors)
- Graceful degradation (optional API, never crashes)
- Session management pattern from KISBroker
- Comprehensive README with setup guide and troubleshooting

Follows NewsAPI pattern for optional APIs.
Uses existing aiohttp dependency.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/notifications/README.md

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+# Telegram Notifications
+
+Real-time trading event notifications via Telegram Bot API.
+
+## Setup
+
+### 1. Create a Telegram Bot
+
+1. Open Telegram and message [@BotFather](https://t.me/BotFather)
+2. Send `/newbot` command
+3. Follow prompts to name your bot
+4. Save the **bot token** (looks like `1234567890:ABCdefGHIjklMNOpqrsTUVwxyz`)
+
+### 2. Get Your Chat ID
+
+**Option A: Using @userinfobot**
+1. Message [@userinfobot](https://t.me/userinfobot) on Telegram
+2. Send `/start`
+3. Save your numeric **chat ID** (e.g., `123456789`)
+
+**Option B: Using @RawDataBot**
+1. Message [@RawDataBot](https://t.me/rawdatabot) on Telegram
+2. Look for `"id":` in the JSON response
+3. Save your numeric **chat ID**
+
+### 3. Configure Environment
+
+Add to your `.env` file:
+
+```bash
+TELEGRAM_BOT_TOKEN=1234567890:ABCdefGHIjklMNOpqrsTUVwxyz
+TELEGRAM_CHAT_ID=123456789
+TELEGRAM_ENABLED=true
+```
+
+### 4. Test the Bot
+
+Start a conversation with your bot on Telegram first (send `/start`), then run:
+
+```bash
+python -m src.main --mode=paper
+```
+
+You should receive a startup notification.
+
+## Message Examples
+
+### Trade Execution
+```
+🟢 BUY
+Symbol: AAPL (United States)
+Quantity: 10 shares
+Price: 150.25
+Confidence: 85%
+```
+
+### Circuit Breaker
+```
+🚨 CIRCUIT BREAKER TRIPPED
+P&L: -3.15% (threshold: -3.0%)
+Trading halted for safety
+```
+
+### Fat-Finger Protection
+```
+⚠️ Fat-Finger Protection
+Order rejected: TSLA
+Attempted: 45.0% of cash
+Max allowed: 30%
+Amount: 45,000 / 100,000
+```
+
+### Market Open/Close
+```
+ℹ️ Market Open
+Korea trading session started
+
+ℹ️ Market Close
+Korea trading session ended
+📈 P&L: +1.25%
+```
+
+### System Status
+```
+📝 System Started
+Mode: PAPER
+Markets: KRX, NASDAQ
+
+System Shutdown
+Normal shutdown
+```
+
+## Notification Priorities
+
+| Priority | Emoji | Use Case |
+|----------|-------|----------|
+| LOW | ℹ️ | Market open/close |
+| MEDIUM | 📊 | Trade execution, system start/stop |
+| HIGH | ⚠️ | Fat-finger protection, errors |
+| CRITICAL | 🚨 | Circuit breaker trips |
+
+## Rate Limiting
+
+- Default: 1 message per second
+- Prevents hitting Telegram's global rate limits
+- Configurable via `rate_limit` parameter
+
+## Troubleshooting
+
+### No notifications received
+
+1. **Check bot configuration**
+   ```bash
+   # Verify env variables are set
+   grep TELEGRAM .env
+   ```
+
+2. **Start conversation with bot**
+   - Open bot in Telegram
+   - Send `/start` command
+   - Bot cannot message users who haven't started a conversation
+
+3. **Check logs**
+   ```bash
+   # Look for Telegram-related errors
+   python -m src.main --mode=paper 2>&1 | grep -i telegram
+   ```
+
+4. **Verify bot token**
+   ```bash
+   curl https://api.telegram.org/bot<YOUR_TOKEN>/getMe
+   # Should return bot info (not 401 error)
+   ```
+
+5. **Verify chat ID**
+   ```bash
+   curl -X POST https://api.telegram.org/bot<YOUR_TOKEN>/sendMessage \
+     -H 'Content-Type: application/json' \
+     -d '{"chat_id": "<YOUR_CHAT_ID>", "text": "Test"}'
+   # Should send a test message
+   ```
+
+### Notifications delayed
+
+- Check rate limiter settings
+- Verify network connection
+- Look for timeout errors in logs
+
+### "Chat not found" error
+
+- Incorrect chat ID
+- Bot blocked by user
+- Need to send `/start` to bot first
+
+### "Unauthorized" error
+
+- Invalid bot token
+- Token revoked (regenerate with @BotFather)
+
+## Graceful Degradation
+
+The system works without Telegram notifications:
+
+- Missing credentials → notifications disabled automatically
+- API errors → logged but trading continues
+- Network timeouts → trading loop unaffected
+- Rate limiting → messages queued, trading proceeds
+
+**Notifications never crash the trading system.**
+
+## Security Notes
+
+- Never commit `.env` file with credentials
+- Bot token grants full bot control
+- Chat ID is not sensitive (just a number)
+- Messages are sent over HTTPS
+- No trading credentials in notifications
+
+## Advanced Usage
+
+### Group Notifications
+
+1. Add bot to Telegram group
+2. Get group chat ID (negative number like `-123456789`)
+3. Use group chat ID in `TELEGRAM_CHAT_ID`
+
+### Multiple Recipients
+
+Create multiple bots or use a broadcast group with multiple members.
+
+### Custom Rate Limits
+
+Not currently exposed in config, but can be modified in code:
+
+```python
+telegram = TelegramClient(
+    bot_token=settings.TELEGRAM_BOT_TOKEN,
+    chat_id=settings.TELEGRAM_CHAT_ID,
+    rate_limit=2.0,  # 2 messages per second
+)
+```
+
+## API Reference
+
+See `telegram_client.py` for full API documentation.
+
+Key methods:
+- `notify_trade_execution()` - Trade alerts
+- `notify_circuit_breaker()` - Emergency stops
+- `notify_fat_finger()` - Order rejections
+- `notify_market_open/close()` - Session tracking
+- `notify_system_start/shutdown()` - Lifecycle events
+- `notify_error()` - Error alerts

src/notifications/__init__.py

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+"""Real-time notifications for trading events."""
+
+from src.notifications.telegram_client import TelegramClient
+
+__all__ = ["TelegramClient"]

src/notifications/telegram_client.py

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+"""Telegram notification client for real-time trading alerts."""
+
+import asyncio
+import logging
+import time
+from dataclasses import dataclass
+from enum import Enum
+
+import aiohttp
+
+logger = logging.getLogger(__name__)
+
+
+class NotificationPriority(Enum):
+    """Priority levels for notifications with emoji indicators."""
+
+    LOW = ("ℹ️", "info")
+    MEDIUM = ("📊", "medium")
+    HIGH = ("⚠️", "warning")
+    CRITICAL = ("🚨", "critical")
+
+    def __init__(self, emoji: str, label: str) -> None:
+        self.emoji = emoji
+        self.label = label
+
+
+class LeakyBucket:
+    """Rate limiter using leaky bucket algorithm."""
+
+    def __init__(self, rate: float, capacity: int = 1) -> None:
+        """
+        Initialize rate limiter.
+
+        Args:
+            rate: Maximum requests per second
+            capacity: Bucket capacity (burst size)
+        """
+        self._rate = rate
+        self._capacity = capacity
+        self._tokens = float(capacity)
+        self._last_update = time.monotonic()
+        self._lock = asyncio.Lock()
+
+    async def acquire(self) -> None:
+        """Wait until a token is available, then consume it."""
+        async with self._lock:
+            now = time.monotonic()
+            elapsed = now - self._last_update
+            self._tokens = min(self._capacity, self._tokens + elapsed * self._rate)
+            self._last_update = now
+
+            if self._tokens < 1.0:
+                wait_time = (1.0 - self._tokens) / self._rate
+                await asyncio.sleep(wait_time)
+                self._tokens = 0.0
+            else:
+                self._tokens -= 1.0
+
+
+@dataclass
+class NotificationMessage:
+    """Internal notification message structure."""
+
+    priority: NotificationPriority
+    message: str
+
+
+class TelegramClient:
+    """Telegram Bot API client for sending trading notifications."""
+
+    API_BASE = "https://api.telegram.org/bot{token}"
+    DEFAULT_TIMEOUT = 5.0  # seconds
+    DEFAULT_RATE = 1.0  # messages per second
+
+    def __init__(
+        self,
+        bot_token: str | None = None,
+        chat_id: str | None = None,
+        enabled: bool = True,
+        rate_limit: float = DEFAULT_RATE,
+    ) -> None:
+        """
+        Initialize Telegram client.
+
+        Args:
+            bot_token: Telegram bot token from @BotFather
+            chat_id: Target chat ID (user or group)
+            enabled: Enable/disable notifications globally
+            rate_limit: Maximum messages per second
+        """
+        self._bot_token = bot_token
+        self._chat_id = chat_id
+        self._enabled = enabled
+        self._rate_limiter = LeakyBucket(rate=rate_limit)
+        self._session: aiohttp.ClientSession | None = None
+
+        if not enabled:
+            logger.info("Telegram notifications disabled via configuration")
+        elif bot_token is None or chat_id is None:
+            logger.warning(
+                "Telegram notifications disabled (missing bot_token or chat_id)"
+            )
+            self._enabled = False
+        else:
+            logger.info("Telegram notifications enabled for chat_id=%s", chat_id)
+
+    def _get_session(self) -> aiohttp.ClientSession:
+        """Get or create aiohttp session."""
+        if self._session is None or self._session.closed:
+            self._session = aiohttp.ClientSession(
+                timeout=aiohttp.ClientTimeout(total=self.DEFAULT_TIMEOUT)
+            )
+        return self._session
+
+    async def close(self) -> None:
+        """Close HTTP session."""
+        if self._session is not None and not self._session.closed:
+            await self._session.close()
+
+    async def _send_notification(self, msg: NotificationMessage) -> None:
+        """
+        Send notification to Telegram with graceful degradation.
+
+        Args:
+            msg: Notification message to send
+        """
+        if not self._enabled:
+            return
+
+        try:
+            await self._rate_limiter.acquire()
+
+            formatted_message = f"{msg.priority.emoji} {msg.message}"
+            url = f"{self.API_BASE.format(token=self._bot_token)}/sendMessage"
+
+            payload = {
+                "chat_id": self._chat_id,
+                "text": formatted_message,
+                "parse_mode": "HTML",
+            }
+
+            session = self._get_session()
+            async with session.post(url, json=payload) as resp:
+                if resp.status != 200:
+                    error_text = await resp.text()
+                    logger.error(
+                        "Telegram API error (status=%d): %s", resp.status, error_text
+                    )
+                else:
+                    logger.debug("Telegram notification sent: %s", msg.message[:50])
+
+        except asyncio.TimeoutError:
+            logger.error("Telegram notification timeout")
+        except aiohttp.ClientError as exc:
+            logger.error("Telegram notification failed: %s", exc)
+        except Exception as exc:
+            logger.error("Unexpected error sending notification: %s", exc)
+
+    async def notify_trade_execution(
+        self,
+        stock_code: str,
+        market: str,
+        action: str,
+        quantity: int,
+        price: float,
+        confidence: float,
+    ) -> None:
+        """
+        Notify trade execution.
+
+        Args:
+            stock_code: Stock ticker symbol
+            market: Market name (e.g., "Korea", "United States")
+            action: "BUY" or "SELL"
+            quantity: Number of shares
+            price: Execution price
+            confidence: AI confidence level (0-100)
+        """
+        emoji = "🟢" if action == "BUY" else "🔴"
+        message = (
+            f"<b>{emoji} {action}</b>\n"
+            f"Symbol: <code>{stock_code}</code> ({market})\n"
+            f"Quantity: {quantity:,} shares\n"
+            f"Price: {price:,.2f}\n"
+            f"Confidence: {confidence:.0f}%"
+        )
+        await self._send_notification(
+            NotificationMessage(priority=NotificationPriority.MEDIUM, message=message)
+        )
+
+    async def notify_market_open(self, market_name: str) -> None:
+        """
+        Notify market opening.
+
+        Args:
+            market_name: Name of the market (e.g., "Korea", "United States")
+        """
+        message = f"<b>Market Open</b>\n{market_name} trading session started"
+        await self._send_notification(
+            NotificationMessage(priority=NotificationPriority.LOW, message=message)
+        )
+
+    async def notify_market_close(self, market_name: str, pnl_pct: float) -> None:
+        """
+        Notify market closing.
+
+        Args:
+            market_name: Name of the market
+            pnl_pct: Final P&L percentage for the session
+        """
+        pnl_sign = "+" if pnl_pct >= 0 else ""
+        pnl_emoji = "📈" if pnl_pct >= 0 else "📉"
+        message = (
+            f"<b>Market Close</b>\n"
+            f"{market_name} trading session ended\n"
+            f"{pnl_emoji} P&L: {pnl_sign}{pnl_pct:.2f}%"
+        )
+        await self._send_notification(
+            NotificationMessage(priority=NotificationPriority.LOW, message=message)
+        )
+
+    async def notify_circuit_breaker(
+        self, pnl_pct: float, threshold: float
+    ) -> None:
+        """
+        Notify circuit breaker activation.
+
+        Args:
+            pnl_pct: Current P&L percentage
+            threshold: Circuit breaker threshold
+        """
+        message = (
+            f"<b>CIRCUIT BREAKER TRIPPED</b>\n"
+            f"P&L: {pnl_pct:.2f}% (threshold: {threshold:.1f}%)\n"
+            f"Trading halted for safety"
+        )
+        await self._send_notification(
+            NotificationMessage(priority=NotificationPriority.CRITICAL, message=message)
+        )
+
+    async def notify_fat_finger(
+        self,
+        stock_code: str,
+        order_amount: float,
+        total_cash: float,
+        max_pct: float,
+    ) -> None:
+        """
+        Notify fat-finger protection rejection.
+
+        Args:
+            stock_code: Stock ticker symbol
+            order_amount: Attempted order amount
+            total_cash: Total available cash
+            max_pct: Maximum allowed percentage
+        """
+        attempted_pct = (order_amount / total_cash) * 100 if total_cash > 0 else 0
+        message = (
+            f"<b>Fat-Finger Protection</b>\n"
+            f"Order rejected: <code>{stock_code}</code>\n"
+            f"Attempted: {attempted_pct:.1f}% of cash\n"
+            f"Max allowed: {max_pct:.0f}%\n"
+            f"Amount: {order_amount:,.0f} / {total_cash:,.0f}"
+        )
+        await self._send_notification(
+            NotificationMessage(priority=NotificationPriority.HIGH, message=message)
+        )
+
+    async def notify_system_start(
+        self, mode: str, enabled_markets: list[str]
+    ) -> None:
+        """
+        Notify system startup.
+
+        Args:
+            mode: Trading mode ("paper" or "live")
+            enabled_markets: List of enabled market codes
+        """
+        mode_emoji = "📝" if mode == "paper" else "💰"
+        markets_str = ", ".join(enabled_markets)
+        message = (
+            f"<b>{mode_emoji} System Started</b>\n"
+            f"Mode: {mode.upper()}\n"
+            f"Markets: {markets_str}"
+        )
+        await self._send_notification(
+            NotificationMessage(priority=NotificationPriority.MEDIUM, message=message)
+        )
+
+    async def notify_system_shutdown(self, reason: str) -> None:
+        """
+        Notify system shutdown.
+
+        Args:
+            reason: Reason for shutdown (e.g., "Normal shutdown", "Circuit breaker")
+        """
+        message = f"<b>System Shutdown</b>\n{reason}"
+        priority = (
+            NotificationPriority.CRITICAL
+            if "circuit breaker" in reason.lower()
+            else NotificationPriority.MEDIUM
+        )
+        await self._send_notification(
+            NotificationMessage(priority=priority, message=message)
+        )
+
+    async def notify_error(
+        self, error_type: str, error_msg: str, context: str
+    ) -> None:
+        """
+        Notify system error.
+
+        Args:
+            error_type: Type of error (e.g., "Connection Error")
+            error_msg: Error message
+            context: Error context (e.g., stock code, market)
+        """
+        message = (
+            f"<b>Error: {error_type}</b>\n"
+            f"Context: {context}\n"
+            f"Message: {error_msg[:200]}"  # Truncate long errors
+        )
+        await self._send_notification(
+            NotificationMessage(priority=NotificationPriority.HIGH, message=message)
+        )