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/activity_provider.dart

@@ -0,0 +1,75 @@
+import 'package:drift/drift.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../database/app_database.dart';
+import 'database_provider.dart';
+
+// ── All activities stream ─────────────────────────────────────────────────────
+
+final activitiesProvider = StreamProvider.autoDispose<List<Activity>>((ref) {
+  return ref.watch(activityDaoProvider).watchAllActivities();
+});
+
+// ── Activity frequency for charts ────────────────────────────────────────────
+
+final activityFrequencyProvider = FutureProvider.autoDispose
+    .family<Map<int, int>, ({DateTime start, DateTime end})>(
+  (ref, range) =>
+      ref.watch(activityDaoProvider).getActivityFrequency(range.start, range.end),
+);
+
+// ── Selected activities (used by log mood screen) ─────────────────────────────
+
+class SelectedActivities extends Notifier<Set<int>> {
+  @override
+  Set<int> build() => {};
+
+  void toggle(int activityId) {
+    if (state.contains(activityId)) {
+      state = <int>{...state}..remove(activityId);
+    } else {
+      state = {...state, activityId};
+    }
+  }
+
+  void clear() => state = {};
+}
+
+final selectedActivitiesProvider =
+    NotifierProvider.autoDispose<SelectedActivities, Set<int>>(
+        SelectedActivities.new);
+
+// ── Activity notifier (create / delete custom activities) ─────────────────────
+
+class ActivityNotifier extends Notifier<AsyncValue<void>> {
+  @override
+  AsyncValue<void> build() => const AsyncData(null);
+
+  Future<void> addActivity({
+    required String name,
+    required int iconCodepoint,
+    required String colourHex,
+  }) async {
+    state = const AsyncLoading();
+    state = await AsyncValue.guard(
+      () => ref.read(activityDaoProvider).insertActivity(
+            ActivitiesCompanion.insert(
+              name: name,
+              iconCodepoint: iconCodepoint,
+              colourHex: colourHex,
+              isCustom: const Value(true),
+            ),
+          ),
+    );
+  }
+
+  Future<void> deleteActivity(int id) async {
+    state = const AsyncLoading();
+    state = await AsyncValue.guard(
+      () => ref.read(activityDaoProvider).deleteActivity(id),
+    );
+  }
+}
+
+final activityNotifierProvider =
+    NotifierProvider.autoDispose<ActivityNotifier, AsyncValue<void>>(
+        ActivityNotifier.new);