feat: implement video job management with retry and delete functionality, enhance video generation status tracking

Co-authored-by: Copilot <copilot@github.com>

backend/app/main.py

@@ -5,7 +5,9 @@ from .routers import ai
 from .routers import generate
 from .routers import images
 from .routers import models
-from .db import close_db, init_db
+from .db import close_db, get_conn, get_write_lock, init_db
+from .services.video_worker import run_worker
+import asyncio
 import os
 from contextlib import asynccontextmanager
 
@@ -19,7 +21,13 @@ load_dotenv()
 @asynccontextmanager
 async def lifespan(app: FastAPI):
     init_db()
+    worker_task = asyncio.create_task(run_worker(get_conn(), get_write_lock()))
     yield
+    worker_task.cancel()
+    try:
+        await worker_task
+    except asyncio.CancelledError:
+        pass
     close_db()