Add complete Ouroboros trading system with TDD test suite

Implement the full autonomous trading agent architecture:
- KIS broker with async API, token refresh, leaky bucket rate limiter, and hash key signing
- Gemini-powered decision engine with JSON parsing and confidence threshold enforcement
- Risk manager with circuit breaker (-3% P&L) and fat finger protection (30% cap)
- Evolution engine for self-improving strategy generation via failure analysis
- 35 passing tests written TDD-first covering risk, broker, and brain modules
- CI/CD pipeline, Docker multi-stage build, and AI agent context docs

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

src/db.py

@@ -0,0 +1,59 @@
+"""Database layer for trade logging."""
+
+from __future__ import annotations
+
+import sqlite3
+from datetime import datetime, timezone
+from typing import Any
+
+
+def init_db(db_path: str) -> sqlite3.Connection:
+    """Initialize the trade logs database and return a connection."""
+    conn = sqlite3.connect(db_path)
+    conn.execute(
+        """
+        CREATE TABLE IF NOT EXISTS trades (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            timestamp TEXT NOT NULL,
+            stock_code TEXT NOT NULL,
+            action TEXT NOT NULL,
+            confidence INTEGER NOT NULL,
+            rationale TEXT,
+            quantity INTEGER,
+            price REAL,
+            pnl REAL DEFAULT 0.0
+        )
+        """
+    )
+    conn.commit()
+    return conn
+
+
+def log_trade(
+    conn: sqlite3.Connection,
+    stock_code: str,
+    action: str,
+    confidence: int,
+    rationale: str,
+    quantity: int = 0,
+    price: float = 0.0,
+    pnl: float = 0.0,
+) -> None:
+    """Insert a trade record into the database."""
+    conn.execute(
+        """
+        INSERT INTO trades (timestamp, stock_code, action, confidence, rationale, quantity, price, pnl)
+        VALUES (?, ?, ?, ?, ?, ?, ?, ?)
+        """,
+        (
+            datetime.now(timezone.utc).isoformat(),
+            stock_code,
+            action,
+            confidence,
+            rationale,
+            quantity,
+            price,
+            pnl,
+        ),
+    )
+    conn.commit()