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.dart

@@ -0,0 +1,42 @@
+import 'package:drift/drift.dart';
+import '../app_database.dart';
+import '../tables.dart';
+
+part 'activity_dao.g.dart';
+
+@DriftAccessor(tables: [Activities, EntryActivities, MoodEntries])
+class ActivityDao extends DatabaseAccessor<AppDatabase>
+    with _$ActivityDaoMixin {
+  ActivityDao(super.db);
+
+  Stream<List<Activity>> watchAllActivities() =>
+      (select(activities)..orderBy([(t) => OrderingTerm.asc(t.sortOrder)]))
+          .watch();
+
+  Future<int> insertActivity(ActivitiesCompanion activity) =>
+      into(activities).insert(activity);
+
+  Future<void> deleteActivity(int id) =>
+      (delete(activities)..where((t) => t.id.equals(id))).go();
+
+  // How many times each activity was logged — used by charts
+  Future<Map<int, int>> getActivityFrequency(
+      DateTime start, DateTime end) async {
+    final entries = await (select(moodEntries)
+          ..where((t) => t.timestamp.isBetweenValues(start, end)))
+        .get();
+    final entryIds = entries.map((e) => e.id).toList();
+
+    if (entryIds.isEmpty) return {};
+
+    final rows = await (select(entryActivities)
+          ..where((t) => t.entryId.isIn(entryIds)))
+        .get();
+
+    final Map<int, int> freq = {};
+    for (final r in rows) {
+      freq[r.activityId] = (freq[r.activityId] ?? 0) + 1;
+    }
+    return freq;
+  }
+}