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.

frontend/src/pages/SetupPage.tsx

@@ -101,20 +101,36 @@ export function SetupPage(): React.JSX.Element {
   const styles = useStyles();
   const navigate = useNavigate();
 
+  const [checking, setChecking] = useState(true);
   const [values, setValues] = useState<FormValues>(DEFAULT_VALUES);
   const [errors, setErrors] = useState<Partial<Record<keyof FormValues, string>>>({});
   const [apiError, setApiError] = useState<string | null>(null);
   const [submitting, setSubmitting] = useState(false);
 
   // Redirect to /login if setup has already been completed.
+  // Show a full-screen spinner while the check is in flight to prevent
+  // the form from flashing before the redirect fires.
   useEffect(() => {
+    let cancelled = false;
     getSetupStatus()
       .then((res) => {
-        if (res.completed) navigate("/login", { replace: true });
+        if (!cancelled) {
+          if (res.completed) {
+            navigate("/login", { replace: true });
+          } else {
+            setChecking(false);
+          }
+        }
       })
       .catch(() => {
-        /* ignore — stay on setup page */
+        // Failed check: the backend may still be starting up. Stay on this
+        // page so the user can attempt setup once the backend is ready.
+        console.warn("SetupPage: setup status check failed — rendering setup form");
+        if (!cancelled) setChecking(false);
       });
+    return (): void => {
+      cancelled = true;
+    };
   }, [navigate]);
 
   // ---------------------------------------------------------------------------
@@ -187,6 +203,21 @@ export function SetupPage(): React.JSX.Element {
   // Render
   // ---------------------------------------------------------------------------
 
+  if (checking) {
+    return (
+      <div
+        style={{
+          display: "flex",
+          justifyContent: "center",
+          alignItems: "center",
+          minHeight: "100vh",
+        }}
+      >
+        <Spinner size="large" label="Loading…" />
+      </div>
+    );
+  }
+
   return (
     <div className={styles.root}>
       <div className={styles.card}>