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/insight_dao.dart

@@ -0,0 +1,26 @@
+import 'package:drift/drift.dart';
+import '../app_database.dart';
+import '../tables.dart';
+
+part 'insight_dao.g.dart';
+
+@DriftAccessor(tables: [LlmInsights])
+class InsightDao extends DatabaseAccessor<AppDatabase> with _$InsightDaoMixin {
+  InsightDao(super.db);
+
+  Future<LlmInsight?> getCached(String promptHash) => (select(llmInsights)
+        ..where((t) => t.promptHash.equals(promptHash))
+        ..limit(1))
+      .getSingleOrNull();
+
+  Future<void> upsertInsight(LlmInsightsCompanion insight) =>
+      into(llmInsights).insertOnConflictUpdate(insight);
+
+  // Purge cached insights older than 7 days
+  Future<void> purgeStale() {
+    final cutoff = DateTime.now().subtract(const Duration(days: 7));
+    return (delete(llmInsights)
+          ..where((t) => t.generatedAt.isSmallerThanValue(cutoff)))
+        .go();
+  }
+}