Flutter startup gate

Stop startup crashes where the UI reads a late field before an async init() has assigned it. The fix is a gate in the root widget: render a splash until initialized, an error screen with retry when init fails, and the app shell only after.

Steps

1. Confirm the race. The crash LateInitializationError: Field 'repo' has not been initialized (or similar) means a widget read a late field in the first frame, before init()'s awaits finished. It may pass on a fast host and only crash on slow real devices — check logcat for E/flutter on-device.
2. Add an init gate to the root widget (app.dart):
   • While initializing → show a splash (logo + spinner + "Opening…").
   • If error != null → show an error screen with a Retry button (do not crash).
   • Only when initialized → show the app shell. Completion criterion: every first-frame widget sits behind the gate; none touch repo/services before the gate opens.
3. Guard against double-init. Add a _initStarted flag so init() can't run twice (hot reload / retry). Expose retryInit() that resets state and re-runs init(). Completion criterion: tapping Retry re-runs init and reaches the shell without a second manual launch.
4. Verify. flutter analyze clean; flutter test passes; reinstall on the real device and confirm logcat shows no LateInitializationError on cold start (see flutter-device-smoke-test).

Reference