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/tables.dart

@@ -0,0 +1,72 @@
+import 'package:drift/drift.dart';
+
+// ─── Mood Entries ────────────────────────────────────────────────────────────
+
+class MoodEntries extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  DateTimeColumn get timestamp => dateTime()();
+  IntColumn get moodLevel => integer()(); // 1–5
+  TextColumn get note => text().nullable()();
+  DateTimeColumn get createdAt => dateTime().withDefault(currentDateAndTime)();
+}
+
+// ─── Activities ──────────────────────────────────────────────────────────────
+
+class Activities extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  TextColumn get name => text().withLength(min: 1, max: 50)();
+  IntColumn get iconCodepoint => integer()(); // Icons codepoint value
+  TextColumn get colourHex =>
+      text().withLength(min: 7, max: 7)(); // e.g. #FF5733
+  BoolColumn get isCustom => boolean().withDefault(const Constant(false))();
+  IntColumn get sortOrder => integer().withDefault(const Constant(0))();
+}
+
+// ─── Entry ↔ Activity (many-to-many) ─────────────────────────────────────────
+
+class EntryActivities extends Table {
+  IntColumn get entryId => integer().references(MoodEntries, #id)();
+  IntColumn get activityId => integer().references(Activities, #id)();
+
+  @override
+  Set<Column> get primaryKey => {entryId, activityId};
+}
+
+// ─── Tags ────────────────────────────────────────────────────────────────────
+
+class Tags extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  TextColumn get name => text().withLength(min: 1, max: 30)();
+  TextColumn get colourHex => text().withLength(min: 7, max: 7)();
+}
+
+// ─── Entry ↔ Tag (many-to-many) ───────────────────────────────────────────────
+
+class EntryTags extends Table {
+  IntColumn get entryId => integer().references(MoodEntries, #id)();
+  IntColumn get tagId => integer().references(Tags, #id)();
+
+  @override
+  Set<Column> get primaryKey => {entryId, tagId};
+}
+
+// ─── LLM Insight Cache ───────────────────────────────────────────────────────
+
+class LlmInsights extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  TextColumn get type => text()(); // 'weekly' | 'monthly' | 'query'
+  TextColumn get promptHash => text()(); // SHA256 of the prompt — cache key
+  TextColumn get responseText => text()();
+  DateTimeColumn get generatedAt =>
+      dateTime().withDefault(currentDateAndTime)();
+  DateTimeColumn get rangeStart => dateTime().nullable()();
+  DateTimeColumn get rangeEnd => dateTime().nullable()();
+}
+
+// ─── Settings ────────────────────────────────────────────────────────────────
+
+class UserSettings extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  TextColumn get key => text().withLength(min: 1, max: 50).unique()();
+  TextColumn get value => text()();
+}