feat: Migrate to MySQL and add unified environment configuration

## Database Migration (SQLite → MySQL)
- Add Alembic migration framework
- Add 'tr_' prefix to all tables to avoid conflicts in shared database
- Remove SQLite support, use MySQL exclusively
- Add pymysql driver dependency
- Change ad_token column to Text type for long JWT tokens

## Unified Environment Configuration
- Centralize all hardcoded settings to environment variables
- Backend: Extend Settings class in app/core/config.py
- Frontend: Use Vite environment variables (import.meta.env)
- Docker: Move credentials to environment variables
- Update .env.example files with comprehensive documentation

## Test Organization
- Move root-level test files to tests/ directory:
  - test_chat_room.py → tests/test_chat_room.py
  - test_websocket.py → tests/test_websocket.py
  - test_realtime_implementation.py → tests/test_realtime_implementation.py
- Fix path references in test_realtime_implementation.py

Breaking Changes:
- CORS now requires explicit origins (no more wildcard)
- All database tables renamed with 'tr_' prefix
- SQLite no longer supported

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/modules/realtime/websocket_manager.py

@@ -6,6 +6,10 @@ import asyncio
 import json
 from collections import defaultdict
 
+from app.core.config import get_settings
+
+settings = get_settings()
+
 
 def json_serializer(obj: Any) -> str:
     """Custom JSON serializer for objects not serializable by default json code"""
@@ -193,9 +197,11 @@ class WebSocketManager:
             if user_id in self._typing_tasks:
                 self._typing_tasks[user_id].cancel()
 
-            # Set new timeout (3 seconds)
+            # Set new timeout (configurable via TYPING_TIMEOUT_SECONDS)
+            typing_timeout = settings.TYPING_TIMEOUT_SECONDS
+
             async def clear_typing():
-                await asyncio.sleep(3)
+                await asyncio.sleep(typing_timeout)
                 self._typing_users[room_id].discard(user_id)
                 if user_id in self._typing_tasks:
                     del self._typing_tasks[user_id]