fix(backend): use background task for startup to avoid blocking server

Change program.startup() to run via asyncio.create_task() so uvicorn
accepts connections immediately while downloader check runs in background.
Also add .claude/ project settings.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/module/api/program.py

@@ -1,3 +1,4 @@
+import asyncio
 import logging
 import os
 import signal
@@ -19,7 +20,7 @@ router = APIRouter(tags=["program"])
 
 @router.on_event("startup")
 async def startup():
-    await program.startup()
+    asyncio.create_task(program.startup())
 
 
 @router.on_event("shutdown")