feat: set up Flutter project with drift database, Riverpod providers, and LLM service layer

- Configure dependencies: drift 2.32.x, flutter_riverpod 3.3.1, fl_chart 1.2.x,
  flutter_local_notifications 21.x, local_auth 3.x, and supporting packages
- Drop riverpod_generator (incompatible analyzer version with drift_dev 2.32.x);
  convert all providers to manual Riverpod 3.x API using Notifier<T> and typed families
- Define drift schema: MoodEntries, Activities, EntryActivities, Tags, EntryTags,
  LlmInsights, UserSettings with four DAOs (mood, activity, insight, settings)
- Add LLM service abstraction (LlmService) and MediaPipe implementation
- Fix SettingsDao.delete → deleteByKey to avoid shadowing drift's inherited delete method

lib/core/providers/database_provider.dart

@@ -0,0 +1,24 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../database/app_database.dart';
+import '../database/daos/mood_dao.dart';
+import '../database/daos/activity_dao.dart';
+import '../database/daos/insight_dao.dart';
+import '../database/daos/settings_dao.dart';
+
+final appDatabaseProvider = Provider<AppDatabase>((ref) {
+  final db = AppDatabase();
+  ref.onDispose(db.close);
+  return db;
+});
+
+final moodDaoProvider =
+    Provider<MoodDao>((ref) => ref.watch(appDatabaseProvider).moodDao);
+
+final activityDaoProvider =
+    Provider<ActivityDao>((ref) => ref.watch(appDatabaseProvider).activityDao);
+
+final insightDaoProvider =
+    Provider<InsightDao>((ref) => ref.watch(appDatabaseProvider).insightDao);
+
+final settingsDaoProvider =
+    Provider<SettingsDao>((ref) => ref.watch(appDatabaseProvider).settingsDao);