feat: wire up app shell, log mood screen, and fix Android build

- Bootstrap ProviderScope in main.dart and move App to app.dart with light/dark theming
- Add initial LogMoodScreen with mood entry flow and shared activity/mood widgets
- Add kIsWeb guard in app_database.dart for drift web support
- Enable Android core library desugaring required by flutter_local_notifications 21.x
- Guard all async notifier state assignments with ref.mounted checks to prevent
  use-after-dispose errors when providers are auto-disposed mid-operation

lib/core/providers/settings_provider.dart

@@ -27,6 +27,7 @@ class SettingsNotifier extends Notifier<AsyncValue<void>> {
 
   Future<void> set(String key, String value) async {
     await ref.read(settingsDaoProvider).set(key, value);
+    if (!ref.mounted) return;
     ref.invalidate(settingProvider(key));
   }