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/mood_provider.dart

@@ -57,7 +57,7 @@ class MoodEntryNotifier extends Notifier<AsyncValue<void>> {
     DateTime? timestamp,
   }) async {
     state = const AsyncLoading();
-    state = await AsyncValue.guard(() async {
+    final next = await AsyncValue.guard(() async {
       final dao = ref.read(moodDaoProvider);
       await dao.insertEntryWithActivities(
         entry: MoodEntriesCompanion.insert(
@@ -69,13 +69,17 @@ class MoodEntryNotifier extends Notifier<AsyncValue<void>> {
         tagIds: tagIds,
       );
     });
+    if (!ref.mounted) return;
+    state = next;
   }
 
   Future<void> deleteEntry(int id) async {
     state = const AsyncLoading();
-    state = await AsyncValue.guard(
+    final next = await AsyncValue.guard(
       () => ref.read(moodDaoProvider).deleteEntry(id),
     );
+    if (!ref.mounted) return;
+    state = next;
   }
 
   Future<void> updateEntry({
@@ -85,7 +89,7 @@ class MoodEntryNotifier extends Notifier<AsyncValue<void>> {
     DateTime? timestamp,
   }) async {
     state = const AsyncLoading();
-    state = await AsyncValue.guard(
+    final next = await AsyncValue.guard(
       () => ref.read(moodDaoProvider).updateEntry(
             MoodEntriesCompanion(
               id: Value(id),
@@ -95,6 +99,8 @@ class MoodEntryNotifier extends Notifier<AsyncValue<void>> {
             ),
           ),
     );
+    if (!ref.mounted) return;
+    state = next;
   }
 }