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>

tests/test_websocket.py

@@ -0,0 +1,98 @@
+#!/usr/bin/env python3
+"""Test WebSocket realtime messaging functionality"""
+import asyncio
+import websockets
+import json
+from datetime import datetime
+
+
+async def test_websocket_connection():
+    """Test basic WebSocket connection and message sending"""
+    # Note: This is a simplified test. In production, you'd need proper authentication
+    uri = "ws://localhost:8000/api/ws/test-room-123?token=test-user@example.com"
+
+    print("Connecting to WebSocket...")
+    try:
+        async with websockets.connect(uri) as websocket:
+            print("✓ Connected to WebSocket!")
+
+            # Send a text message
+            message = {
+                "type": "message",
+                "content": "Hello from WebSocket test!",
+                "message_type": "text"
+            }
+
+            print(f"\nSending message: {message}")
+            await websocket.send(json.dumps(message))
+
+            # Wait for acknowledgment
+            response = await asyncio.wait_for(websocket.recv(), timeout=5)
+            response_data = json.loads(response)
+            print(f"✓ Received response: {response_data}")
+
+            if response_data.get("type") == "ack":
+                print(f"  Message ID: {response_data.get('message_id')}")
+                print(f"  Sequence: {response_data.get('sequence_number')}")
+
+    except websockets.exceptions.InvalidStatusCode as e:
+        if e.status_code == 4001:
+            print("✗ Connection rejected: Not a member of room")
+            print("  This is expected for test room without proper membership")
+        else:
+            print(f"✗ Connection failed with status {e.status_code}")
+    except Exception as e:
+        print(f"✗ Error: {e}")
+
+
+async def test_rest_api():
+    """Test REST API endpoints"""
+    import aiohttp
+
+    print("\n" + "=" * 50)
+    print("Testing REST API Endpoints")
+    print("=" * 50)
+
+    # Note: This requires authentication in production
+    # For now, just test if endpoints are registered
+
+    async with aiohttp.ClientSession() as session:
+        # Test health check
+        async with session.get("http://localhost:8000/health") as resp:
+            if resp.status == 200:
+                print("✓ Health check endpoint working")
+            else:
+                print(f"✗ Health check failed: {resp.status}")
+
+        # Test API docs
+        async with session.get("http://localhost:8000/docs") as resp:
+            if resp.status == 200:
+                print("✓ API documentation accessible")
+            else:
+                print(f"✗ API docs failed: {resp.status}")
+
+
+if __name__ == "__main__":
+    print("=" * 50)
+    print("WebSocket Realtime Messaging Test")
+    print("=" * 50)
+
+    # Run REST API tests
+    asyncio.run(test_rest_api())
+
+    print("\n" + "=" * 50)
+    print("Testing WebSocket Connection")
+    print("=" * 50)
+
+    # Run WebSocket test
+    asyncio.run(test_websocket_connection())
+
+    print("\n" + "=" * 50)
+    print("Test Summary:")
+    print("- Database tables created ✓")
+    print("- Models and schemas defined ✓")
+    print("- WebSocket manager implemented ✓")
+    print("- Message service layer created ✓")
+    print("- REST API endpoints registered ✓")
+    print("- Server starts successfully ✓")
+    print("=" * 50)