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/activity_dao.g.dart

@@ -0,0 +1,23 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'activity_dao.dart';
+
+// ignore_for_file: type=lint
+mixin _$ActivityDaoMixin on DatabaseAccessor<AppDatabase> {
+  $ActivitiesTable get activities => attachedDatabase.activities;
+  $MoodEntriesTable get moodEntries => attachedDatabase.moodEntries;
+  $EntryActivitiesTable get entryActivities => attachedDatabase.entryActivities;
+  ActivityDaoManager get managers => ActivityDaoManager(this);
+}
+
+class ActivityDaoManager {
+  final _$ActivityDaoMixin _db;
+  ActivityDaoManager(this._db);
+  $$ActivitiesTableTableManager get activities =>
+      $$ActivitiesTableTableManager(_db.attachedDatabase, _db.activities);
+  $$MoodEntriesTableTableManager get moodEntries =>
+      $$MoodEntriesTableTableManager(_db.attachedDatabase, _db.moodEntries);
+  $$EntryActivitiesTableTableManager get entryActivities =>
+      $$EntryActivitiesTableTableManager(
+          _db.attachedDatabase, _db.entryActivities);
+}