Add user ping system and room deletion functionality

Backend changes:
- Fix track deletion foreign key constraint (tracks.py)
  * Clear current_track_id from rooms before deleting track
  * Prevent deletion errors when track is currently playing

- Implement user ping/keepalive system (sync.py, websocket.py, ping_task.py, main.py)
  * Track last pong timestamp for each user
  * Background task sends ping every 30s, disconnects users after 60s timeout
  * Auto-pause playback when room becomes empty
  * Remove disconnected users from room_participants

- Enhance room deletion (rooms.py)
  * Broadcast room_deleted event to all connected users
  * Close all WebSocket connections before deletion
  * Cascade delete participants, queue, and messages

Frontend changes:
- Add ping/pong WebSocket handling (activeRoom.js)
  * Auto-respond to server pings
  * Handle room_deleted event with redirect to home

- Add room deletion UI (RoomView.vue, HomeView.vue, RoomCard.vue)
  * Delete button visible only to room owner
  * Confirmation dialog with warning
  * Delete button on room cards (shows on hover)
  * Redirect to home page after deletion

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

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

backend/app/main.py

@@ -9,6 +9,7 @@ from .routers import auth, rooms, tracks, websocket, messages
 from .database import async_session
 from .models.room import Room
 from .services.sync import manager
+from .services.ping_task import ping_users_task
 from .config import get_settings
 
 # Setup logging
@@ -62,15 +63,22 @@ async def periodic_sync():
 
 @asynccontextmanager
 async def lifespan(app: FastAPI):
-    # Start background sync task
+    # Start background tasks
     sync_task = asyncio.create_task(periodic_sync())
+    ping_task = asyncio.create_task(ping_users_task())
+    logger.info("Background tasks started: periodic_sync, ping_users_task")
     yield
     # Cleanup
     sync_task.cancel()
+    ping_task.cancel()
     try:
         await sync_task
     except asyncio.CancelledError:
         pass
+    try:
+        await ping_task
+    except asyncio.CancelledError:
+        pass
 
 
 app = FastAPI(title="EnigFM", description="Listen to music together with friends", lifespan=lifespan)