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/router.py

@@ -7,6 +7,7 @@ from datetime import datetime
 import json
 
 from app.core.database import get_db
+from app.core.config import get_settings
 from app.modules.auth.dependencies import get_current_user
 from app.modules.auth.services.session_service import session_service
 from app.modules.chat_room.models import RoomMember, MemberRole
@@ -32,7 +33,7 @@ from sqlalchemy import and_
 
 router = APIRouter(prefix="/api", tags=["realtime"])
 
-SYSTEM_ADMIN_EMAIL = "ymirliu@panjit.com.tw"
+settings = get_settings()
 
 
 async def ws_send_json(websocket: WebSocket, data: dict):
@@ -51,9 +52,14 @@ def get_user_room_membership(db: Session, room_id: str, user_id: str) -> Optiona
     ).first()
 
 
+def is_system_admin(user_id: str) -> bool:
+    """Check if user is the system administrator"""
+    return bool(settings.SYSTEM_ADMIN_EMAIL and user_id == settings.SYSTEM_ADMIN_EMAIL)
+
+
 def can_write_message(membership: Optional[RoomMember], user_id: str) -> bool:
     """Check if user has write permission (OWNER or EDITOR)"""
-    if user_id == SYSTEM_ADMIN_EMAIL:
+    if is_system_admin(user_id):
         return True
 
     if not membership:
@@ -99,7 +105,7 @@ async def websocket_endpoint(
 
         # Check room membership
         membership = get_user_room_membership(db, room_id, user_id)
-        if not membership and user_id != SYSTEM_ADMIN_EMAIL:
+        if not membership and not is_system_admin(user_id):
             await websocket.close(code=4001, reason="Not a member of this room")
             return
 
@@ -225,12 +231,11 @@ async def websocket_endpoint(
                         continue
 
                     # Delete message
-                    is_admin = user_id == SYSTEM_ADMIN_EMAIL
                     deleted_message = MessageService.delete_message(
                         db=db,
                         message_id=ws_message.message_id,
                         user_id=user_id,
-                        is_admin=is_admin
+                        is_admin=is_system_admin(user_id)
                     )
 
                     if not deleted_message:
@@ -345,7 +350,7 @@ async def get_messages(
 
     # Check room membership
     membership = get_user_room_membership(db, room_id, user_id)
-    if not membership and user_id != SYSTEM_ADMIN_EMAIL:
+    if not membership and not is_system_admin(user_id):
         raise HTTPException(status_code=403, detail="Not a member of this room")
 
     return MessageService.get_messages(
@@ -414,7 +419,7 @@ async def search_messages(
 
     # Check room membership
     membership = get_user_room_membership(db, room_id, user_id)
-    if not membership and user_id != SYSTEM_ADMIN_EMAIL:
+    if not membership and not is_system_admin(user_id):
         raise HTTPException(status_code=403, detail="Not a member of this room")
 
     return MessageService.search_messages(
@@ -437,7 +442,7 @@ async def get_online_users(
 
     # Check room membership
     membership = get_user_room_membership(db, room_id, user_id)
-    if not membership and user_id != SYSTEM_ADMIN_EMAIL:
+    if not membership and not is_system_admin(user_id):
         raise HTTPException(status_code=403, detail="Not a member of this room")
 
     online_users = manager.get_online_users(room_id)
@@ -455,7 +460,7 @@ async def get_typing_users(
 
     # Check room membership
     membership = get_user_room_membership(db, room_id, user_id)
-    if not membership and user_id != SYSTEM_ADMIN_EMAIL:
+    if not membership and not is_system_admin(user_id):
         raise HTTPException(status_code=403, detail="Not a member of this room")
 
     typing_users = manager.get_typing_users(room_id)