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/routers/websocket.py

@@ -63,6 +63,11 @@ async def room_websocket(websocket: WebSocket, room_id: UUID):
                 await websocket.send_json({"type": "pong"})
                 continue
 
+            # Handle pong response (from server ping)
+            if message.get("type") == "pong":
+                manager.update_pong(room_id, user.id)
+                continue
+
             async with async_session() as db:
                 if message["type"] == "player_action":
                     await handle_player_action(db, room_id, user, message)
@@ -72,11 +77,50 @@ async def room_websocket(websocket: WebSocket, room_id: UUID):
                     await handle_sync_request(db, room_id, websocket)
 
     except WebSocketDisconnect:
-        manager.disconnect(websocket, room_id, user.id)
-        await manager.broadcast_to_room(
-            room_id,
-            {"type": "user_left", "user_id": str(user.id)},
+        await handle_user_disconnect(websocket, room_id, user.id)
+
+
+async def handle_user_disconnect(websocket: WebSocket, room_id: UUID, user_id: UUID):
+    """Обработка отключения пользователя от комнаты"""
+    manager.disconnect(websocket, room_id, user_id)
+
+    # Удаляем пользователя из participants в БД
+    async with async_session() as db:
+        await db.execute(
+            select(RoomParticipant)
+            .where(RoomParticipant.room_id == room_id)
+            .where(RoomParticipant.user_id == user_id)
         )
+        await db.execute(
+            RoomParticipant.__table__.delete().where(
+                RoomParticipant.room_id == room_id,
+                RoomParticipant.user_id == user_id
+            )
+        )
+        await db.commit()
+
+        # Проверяем, остались ли участники в комнате
+        room_user_count = manager.get_room_user_count(room_id)
+
+        # Если комната пустая - ставим трек на паузу
+        if room_user_count == 0:
+            result = await db.execute(select(Room).where(Room.id == room_id))
+            room = result.scalar_one_or_none()
+            if room and room.is_playing:
+                # Сохраняем текущую позицию
+                if room.playback_started_at:
+                    elapsed = (datetime.utcnow() - room.playback_started_at).total_seconds() * 1000
+                    room.playback_position = int((room.playback_position or 0) + elapsed)
+
+                room.is_playing = False
+                room.playback_started_at = None
+                await db.commit()
+
+    # Уведомляем остальных участников
+    await manager.broadcast_to_room(
+        room_id,
+        {"type": "user_left", "user_id": str(user_id)},
+    )
 
 
 async def handle_player_action(db: AsyncSession, room_id: UUID, user: User, message: dict):