feat: add configuration and documentation for Telegram commands (issue #69)

Add configuration options and comprehensive documentation for the new
bidirectional command feature.

Changes:
- Add TELEGRAM_COMMANDS_ENABLED to config.py
- Add TELEGRAM_POLLING_INTERVAL to config.py
- Add extensive "Bidirectional Commands" section to README.md

Documentation:
- Available commands table with descriptions
- Command usage examples with sample outputs
- Security section (Chat ID verification, authorization)
- Configuration options and .env examples
- How it works (long polling, authentication flow)
- Error handling and troubleshooting guide

Features:
- Optional command support (can disable while keeping notifications)
- Configurable polling interval
- Complete security documentation
- Troubleshooting guide for common issues

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

src/config.py

@@ -66,6 +66,10 @@ class Settings(BaseSettings):
     TELEGRAM_CHAT_ID: str | None = None
     TELEGRAM_ENABLED: bool = True
 
+    # Telegram Commands (optional)
+    TELEGRAM_COMMANDS_ENABLED: bool = True
+    TELEGRAM_POLLING_INTERVAL: float = 1.0  # seconds
+
     model_config = {"env_file": ".env", "env_file_encoding": "utf-8"}
 
     @property