Fix Stage 0 bootstrap and startup regression

Task 0.1: Create database parent directory before connecting
- main.py _lifespan now calls Path(database_path).parent.mkdir(parents=True,
  exist_ok=True) before aiosqlite.connect() so the app starts cleanly on
  a fresh Docker volume with a nested database path.

Task 0.2: SetupRedirectMiddleware redirects when db is None
- Guard now reads: if db is None or not is_setup_complete(db)
  A missing database (startup still in progress) is treated as setup not
  complete instead of silently allowing all API routes through.

Task 0.3: SetupGuard redirects to /setup on API failure
- .catch() handler now sets status to 'pending' instead of 'done'.
  A crashed backend cannot serve protected routes; conservative fallback
  is to redirect to /setup.

Task 0.4: SetupPage shows spinner while checking setup status
- Added 'checking' boolean state; full-screen Spinner is rendered until
  getSetupStatus() resolves, preventing form flash before redirect.
- Added console.warn in catch block; cleanup return added to useEffect.

Also: remove unused type: ignore[call-arg] from config.py.

Tests: 18 backend tests pass; 117 frontend tests pass.

backend/app/main.py

@@ -138,6 +138,9 @@ async def _lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
     log.info("bangui_starting_up", database_path=settings.database_path)
 
     # --- Application database ---
+    db_path: Path = Path(settings.database_path)
+    db_path.parent.mkdir(parents=True, exist_ok=True)
+    log.debug("database_directory_ensured", directory=str(db_path.parent))
     db: aiosqlite.Connection = await aiosqlite.connect(settings.database_path)
     db.row_factory = aiosqlite.Row
     await init_db(db)
@@ -320,17 +323,15 @@ class SetupRedirectMiddleware(BaseHTTPMiddleware):
         if path.startswith("/api") and not getattr(
             request.app.state, "_setup_complete_cached", False
         ):
-            db: aiosqlite.Connection | None = getattr(request.app.state, "db", None)
-            if db is not None:
-                from app.services import setup_service  # noqa: PLC0415
+            from app.services import setup_service  # noqa: PLC0415
 
-                if await setup_service.is_setup_complete(db):
-                    request.app.state._setup_complete_cached = True
-                else:
-                    return RedirectResponse(
-                        url="/api/setup",
-                        status_code=status.HTTP_307_TEMPORARY_REDIRECT,
-                    )
+            db: aiosqlite.Connection | None = getattr(request.app.state, "db", None)
+            if db is None or not await setup_service.is_setup_complete(db):
+                return RedirectResponse(
+                    url="/api/setup",
+                    status_code=status.HTTP_307_TEMPORARY_REDIRECT,
+                )
+            request.app.state._setup_complete_cached = True
 
         return await call_next(request)