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/insight_provider.dart

@@ -0,0 +1,73 @@
+import 'dart:convert';
+import 'package:crypto/crypto.dart';
+import 'package:drift/drift.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../database/app_database.dart';
+import 'database_provider.dart';
+
+// ── Insight type enum ─────────────────────────────────────────────────────────
+
+enum InsightType { weekly, monthly, query }
+
+// ── Cached insight lookup ─────────────────────────────────────────────────────
+
+final cachedInsightProvider =
+    FutureProvider.autoDispose.family<LlmInsight?, String>((ref, promptHash) {
+  return ref.watch(insightDaoProvider).getCached(promptHash);
+});
+
+// ── Insight notifier — triggers generation and caches results ─────────────────
+
+class InsightNotifier extends Notifier<AsyncValue<String?>> {
+  @override
+  AsyncValue<String?> build() => const AsyncData(null);
+
+  String _hashPrompt(String prompt) =>
+      sha256.convert(utf8.encode(prompt)).toString();
+
+  Future<void> generateInsight({
+    required String prompt,
+    required InsightType type,
+    DateTime? rangeStart,
+    DateTime? rangeEnd,
+  }) async {
+    state = const AsyncLoading();
+
+    final hash = _hashPrompt(prompt);
+    final dao = ref.read(insightDaoProvider);
+
+    final cached = await dao.getCached(hash);
+    if (cached != null) {
+      state = AsyncData(cached.responseText);
+      return;
+    }
+
+    // Generation happens in LlmNotifier (see llm_provider.dart)
+    state = const AsyncData(null);
+  }
+
+  Future<void> saveInsight({
+    required String promptHash,
+    required String responseText,
+    required InsightType type,
+    DateTime? rangeStart,
+    DateTime? rangeEnd,
+  }) async {
+    await ref.read(insightDaoProvider).upsertInsight(
+          LlmInsightsCompanion.insert(
+            type: type.name,
+            promptHash: promptHash,
+            responseText: responseText,
+            rangeStart: Value(rangeStart),
+            rangeEnd: Value(rangeEnd),
+          ),
+        );
+    state = AsyncData(responseText);
+  }
+
+  void clear() => state = const AsyncData(null);
+}
+
+final insightNotifierProvider =
+    NotifierProvider.autoDispose<InsightNotifier, AsyncValue<String?>>(
+        InsightNotifier.new);