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/data/api/notes_api.dart

@@ -27,11 +27,18 @@ class NotesApi {
     }
   }
 
-  Future<Note> create(String title, String body) async {
+  Future<Note> create(
+    String title,
+    String body, {
+    List<String> tags = const [],
+    int? projectId,
+  }) async {
     try {
       final response = await _dio.post('/api/notes', data: {
         'title': title,
         'body': body,
+        'tags': tags,
+        if (projectId != null) 'project_id': projectId,
       });
       return Note.fromJson(response.data as Map<String, dynamic>);
     } on DioException catch (e) {
@@ -39,11 +46,20 @@ class NotesApi {
     }
   }
 
-  Future<Note> update(int id, String title, String body) async {
+  Future<Note> update(
+    int id,
+    String title,
+    String body, {
+    List<String> tags = const [],
+    int? projectId,
+    bool clearProject = false,
+  }) async {
     try {
       final response = await _dio.put('/api/notes/$id', data: {
         'title': title,
         'body': body,
+        'tags': tags,
+        if (clearProject) 'project_id': null else if (projectId != null) 'project_id': projectId,
       });
       return Note.fromJson(response.data as Map<String, dynamic>);
     } on DioException catch (e) {