feat(offline): tier 2 phase 2 — extend cache to tasks/projects/milestones/events/conversations

Phase 1 cached only notes. Phase 2 brings the read-through pattern to every
domain the app reads in bulk:

- Drift schema v2: 5 new cached_* tables + onUpgrade migration. Calendar
  events use range-scoped read/write (replaceEventsInRange) so disjoint
  month fetches don't clobber each other; milestones are per-project.
- Wrap TasksRepository, ProjectsRepository, MilestonesRepository, and
  ChatRepository (conversation list only) with NetworkException fallback.
  Writes hit the API then sync the cache.
- New EventsRepository wrapping EventsApi; calendar_provider and
  event_form_sheet repointed at the repository.
- OfflineBanner now surfaces getLatestSync() — most-recent timestamp
  across all domains — so the hint reads sensibly regardless of screen.

flutter analyze clean; existing tests pass. Phase 3 (offline write queue)
and Phase 4 (read-only UI indicators) still to come.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/providers/api_client_provider.dart

@@ -18,6 +18,7 @@ import '../data/api/tasks_api.dart';
 import '../data/local/database.dart';
 import '../data/repositories/auth_repository.dart';
 import '../data/repositories/chat_repository.dart';
+import '../data/repositories/events_repository.dart';
 import '../data/repositories/knowledge_repository.dart';
 import '../data/repositories/voice_repository.dart';
 import '../data/repositories/milestones_repository.dart';
@@ -82,15 +83,24 @@ final notesRepositoryProvider = Provider<NotesRepository>((ref) {
 });
 
 final tasksRepositoryProvider = Provider<TasksRepository>((ref) {
-  return TasksRepository(ref.watch(tasksApiProvider));
+  return TasksRepository(
+    ref.watch(tasksApiProvider),
+    ref.watch(fabledDatabaseProvider),
+  );
 });
 
 final chatRepositoryProvider = Provider<ChatRepository>((ref) {
-  return ChatRepository(ref.watch(chatApiProvider));
+  return ChatRepository(
+    ref.watch(chatApiProvider),
+    ref.watch(fabledDatabaseProvider),
+  );
 });
 
 final projectsRepositoryProvider = Provider<ProjectsRepository>((ref) {
-  return ProjectsRepository(ref.watch(projectsApiProvider));
+  return ProjectsRepository(
+    ref.watch(projectsApiProvider),
+    ref.watch(fabledDatabaseProvider),
+  );
 });
 
 final milestonesApiProvider = Provider<MilestonesApi>((ref) {
@@ -98,7 +108,10 @@ final milestonesApiProvider = Provider<MilestonesApi>((ref) {
 });
 
 final milestonesRepositoryProvider = Provider<MilestonesRepository>((ref) {
-  return MilestonesRepository(ref.watch(milestonesApiProvider));
+  return MilestonesRepository(
+    ref.watch(milestonesApiProvider),
+    ref.watch(fabledDatabaseProvider),
+  );
 });
 
 final knowledgeApiProvider = Provider<KnowledgeApi>((ref) {
@@ -128,3 +141,10 @@ final voiceRepositoryProvider = Provider<VoiceRepository>((ref) {
 final eventsApiProvider = Provider<EventsApi>((ref) {
   return EventsApi(ref.watch(dioProvider));
 });
+
+final eventsRepositoryProvider = Provider<EventsRepository>((ref) {
+  return EventsRepository(
+    ref.watch(eventsApiProvider),
+    ref.watch(fabledDatabaseProvider),
+  );
+});

lib/providers/calendar_provider.dart

@@ -47,7 +47,7 @@ class CalendarNotifier extends AsyncNotifier<CalendarState> {
     // Fetch current month ± 1 month as the initial window.
     final from = DateTime(now.year, now.month - 1, 1);
     final to = DateTime(now.year, now.month + 2, 0, 23, 59, 59);
-    final events = await ref.watch(eventsApiProvider).getEvents(from, to);
+    final events = await ref.watch(eventsRepositoryProvider).getEvents(from, to);
     return CalendarState(
       eventsByDay: _groupByDay(events),
       selectedDay: today,
@@ -60,7 +60,7 @@ class CalendarNotifier extends AsyncNotifier<CalendarState> {
   Future<void> refresh() async {
     final current = state.value;
     if (current == null) return;
-    final events = await ref.read(eventsApiProvider).getEvents(
+    final events = await ref.read(eventsRepositoryProvider).getEvents(
       current.loadedRange.start,
       current.loadedRange.end,
     );
@@ -93,7 +93,7 @@ class CalendarNotifier extends AsyncNotifier<CalendarState> {
     try {
       final from = DateTime(month.year, month.month, 1);
       final to = DateTime(month.year, month.month + 1, 0, 23, 59, 59);
-      final events = await ref.read(eventsApiProvider).getEvents(from, to);
+      final events = await ref.read(eventsRepositoryProvider).getEvents(from, to);
       final s = state.value!;
       final merged = Map<DateTime, List<CalendarEvent>>.from(s.eventsByDay);
       for (final e in events) {