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/llm_provider.dart

@@ -0,0 +1,55 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../llm/llm_service.dart';
+import '../llm/mediapipe_llm_service.dart';
+
+// ── Service singleton ─────────────────────────────────────────────────────────
+
+final llmServiceProvider = Provider<LlmService>((ref) {
+  final service = MediapipeLlmService();
+  ref.onDispose(service.dispose);
+  return service;
+});
+
+// ── Model initialisation state ────────────────────────────────────────────────
+
+final llmReadyProvider = FutureProvider<void>((ref) async {
+  await ref.watch(llmServiceProvider).initialise();
+});
+
+// ── Streaming response notifier ───────────────────────────────────────────────
+
+class LlmResponseNotifier extends Notifier<AsyncValue<String>> {
+  bool _cancelled = false;
+
+  @override
+  AsyncValue<String> build() => const AsyncData('');
+
+  Future<void> generate(String prompt) async {
+    _cancelled = false;
+    state = const AsyncLoading();
+
+    final service = ref.read(llmServiceProvider);
+    final buffer = StringBuffer();
+
+    try {
+      await for (final token in service.generateStream(prompt)) {
+        if (_cancelled) break;
+        buffer.write(token);
+        state = AsyncData(buffer.toString());
+      }
+    } catch (e, st) {
+      state = AsyncError(e, st);
+    }
+  }
+
+  void cancel() {
+    _cancelled = true;
+    state = const AsyncData('');
+  }
+
+  void clear() => state = const AsyncData('');
+}
+
+final llmResponseNotifierProvider =
+    NotifierProvider.autoDispose<LlmResponseNotifier, AsyncValue<String>>(
+        LlmResponseNotifier.new);