Add Projects feature; sync Note/Task models with backend additions

## New: Projects
- Project model, API, repository, Riverpod provider
- ProjectListScreen: active/archived sections, create dialog, long-press status/delete
- ProjectSelector widget: DropdownButtonFormField for note + task editors
- Projects tab added to shell (bottom nav + navigation rail, 4th position)
- /projects route registered in GoRouter ShellRoute

## Updated: Note model
- Added tags: List<String>, projectId: int?, milestoneId: int?
- NotesApi.create/update pass tags and project_id
- NotesRepository and NotesNotifier signatures updated
- NoteEditScreen: chip-based tag input + ProjectSelector

## Updated: Task model
- Added projectId: int?, milestoneId: int?, parentId: int?
- TasksApi.create passes project_id; update payload includes project_id
- TasksRepository and TasksNotifier signatures updated
- TaskEditScreen: ProjectSelector added; project_id sent on save

## Provider fix
- ProjectsNotifier.update renamed to updateProject to avoid conflict
  with AsyncNotifier.update(FutureOr<State> Function(State)) base method

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/providers/api_client_provider.dart

@@ -6,11 +6,13 @@ import '../data/api/api_client.dart';
 import '../data/api/auth_api.dart';
 import '../data/api/chat_api.dart';
 import '../data/api/notes_api.dart';
+import '../data/api/projects_api.dart';
 import '../data/api/quick_capture_api.dart';
 import '../data/api/tasks_api.dart';
 import '../data/repositories/auth_repository.dart';
 import '../data/repositories/chat_repository.dart';
 import '../data/repositories/notes_repository.dart';
+import '../data/repositories/projects_repository.dart';
 import '../data/repositories/tasks_repository.dart';
 import 'settings_provider.dart';
 
@@ -45,6 +47,10 @@ final quickCaptureApiProvider = Provider<QuickCaptureApi>((ref) {
   return QuickCaptureApi(ref.watch(dioProvider));
 });
 
+final projectsApiProvider = Provider<ProjectsApi>((ref) {
+  return ProjectsApi(ref.watch(dioProvider));
+});
+
 final authRepositoryProvider = Provider<AuthRepository>((ref) {
   return AuthRepository(ref.watch(authApiProvider));
 });
@@ -60,3 +66,7 @@ final tasksRepositoryProvider = Provider<TasksRepository>((ref) {
 final chatRepositoryProvider = Provider<ChatRepository>((ref) {
   return ChatRepository(ref.watch(chatApiProvider));
 });
+
+final projectsRepositoryProvider = Provider<ProjectsRepository>((ref) {
+  return ProjectsRepository(ref.watch(projectsApiProvider));
+});