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/insight_provider.dart

@@ -37,6 +37,7 @@ class InsightNotifier extends Notifier<AsyncValue<String?>> {
     final dao = ref.read(insightDaoProvider);
 
     final cached = await dao.getCached(hash);
+    if (!ref.mounted) return;
     if (cached != null) {
       state = AsyncData(cached.responseText);
       return;
@@ -62,6 +63,7 @@ class InsightNotifier extends Notifier<AsyncValue<String?>> {
             rangeEnd: Value(rangeEnd),
           ),
         );
+    if (!ref.mounted) return;
     state = AsyncData(responseText);
   }