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/database/daos/settings_dao.dart

@@ -0,0 +1,27 @@
+import 'package:drift/drift.dart';
+import '../app_database.dart';
+import '../tables.dart';
+
+part 'settings_dao.g.dart';
+
+@DriftAccessor(tables: [UserSettings])
+class SettingsDao extends DatabaseAccessor<AppDatabase>
+    with _$SettingsDaoMixin {
+  SettingsDao(super.db);
+
+  Future<String?> get(String key) async {
+    final row = await (select(userSettings)
+          ..where((t) => t.key.equals(key))
+          ..limit(1))
+        .getSingleOrNull();
+    return row?.value;
+  }
+
+  Future<void> set(String key, String value) =>
+      into(userSettings).insertOnConflictUpdate(
+        UserSettingsCompanion.insert(key: key, value: value),
+      );
+
+  Future<void> deleteByKey(String key) =>
+      (delete(userSettings)..where((t) => t.key.equals(key))).go();
+}