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/app.dart

@@ -17,6 +17,7 @@ import 'screens/chat/conversations_list_screen.dart';
 import 'screens/notes/note_detail_screen.dart';
 import 'screens/notes/note_edit_screen.dart';
 import 'screens/notes/notes_list_screen.dart';
+import 'screens/projects/project_list_screen.dart';
 import 'screens/settings/settings_screen.dart';
 import 'screens/setup/setup_screen.dart';
 import 'screens/splash/splash_screen.dart';
@@ -118,6 +119,10 @@ final routerProvider = Provider<GoRouter>((ref) {
             path: Routes.tasks,
             builder: (_, _) => const TasksListScreen(),
           ),
+          GoRoute(
+            path: Routes.projects,
+            builder: (_, _) => const ProjectListScreen(),
+          ),
           GoRoute(
             path: Routes.conversations,
             builder: (_, _) => const ConversationsListScreen(),
@@ -137,7 +142,7 @@ class _Shell extends ConsumerStatefulWidget {
 }
 
 class _ShellState extends ConsumerState<_Shell> {
-  static const _tabs = [Routes.notes, Routes.tasks, Routes.conversations];
+  static const _tabs = [Routes.notes, Routes.tasks, Routes.projects, Routes.conversations];
 
   @override
   void initState() {
@@ -253,6 +258,11 @@ class _ShellState extends ConsumerState<_Shell> {
                           selectedIcon: Icon(Icons.check_box),
                           label: Text('Tasks'),
                         ),
+                        NavigationRailDestination(
+                          icon: Icon(Icons.folder_outlined),
+                          selectedIcon: Icon(Icons.folder),
+                          label: Text('Projects'),
+                        ),
                         NavigationRailDestination(
                           icon: Icon(Icons.chat_bubble_outline),
                           selectedIcon: Icon(Icons.chat_bubble),
@@ -284,6 +294,7 @@ class _ShellState extends ConsumerState<_Shell> {
         destinations: const [
           NavigationDestination(icon: Icon(Icons.note), label: 'Notes'),
           NavigationDestination(icon: Icon(Icons.check_box), label: 'Tasks'),
+          NavigationDestination(icon: Icon(Icons.folder), label: 'Projects'),
           NavigationDestination(
               icon: Icon(Icons.chat_bubble), label: 'Chat'),
         ],