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/config.py

@@ -85,4 +85,4 @@ def get_settings() -> Settings:
         A validated :class:`Settings` object. Raises :class:`pydantic.ValidationError`
         if required keys are absent or values fail validation.
     """
-    return Settings()  # type: ignore[call-arg]  # pydantic-settings populates required fields from env vars
+    return Settings()  # pydantic-settings populates required fields from env vars