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/repositories/notes_repository.dart

@@ -7,9 +7,25 @@ class NotesRepository {
 
   Future<List<Note>> getAll() => _api.getAll();
   Future<Note> getOne(int id) => _api.getOne(id);
-  Future<Note> create(String title, String body) =>
-      _api.create(title, body);
-  Future<Note> update(int id, String title, String body) =>
-      _api.update(id, title, body);
+
+  Future<Note> create(
+    String title,
+    String body, {
+    List<String> tags = const [],
+    int? projectId,
+  }) =>
+      _api.create(title, body, tags: tags, projectId: projectId);
+
+  Future<Note> update(
+    int id,
+    String title,
+    String body, {
+    List<String> tags = const [],
+    int? projectId,
+    bool clearProject = false,
+  }) =>
+      _api.update(id, title, body,
+          tags: tags, projectId: projectId, clearProject: clearProject);
+
   Future<void> delete(int id) => _api.delete(id);
 }

lib/data/repositories/projects_repository.dart

@@ -0,0 +1,21 @@
+import '../api/projects_api.dart';
+import '../models/project.dart';
+
+class ProjectsRepository {
+  final ProjectsApi _api;
+  const ProjectsRepository(this._api);
+
+  Future<List<Project>> getAll({String? status}) => _api.getAll(status: status);
+  Future<Project> getOne(int id) => _api.getOne(id);
+  Future<Project> create({
+    required String title,
+    String? description,
+    String? goal,
+    String? color,
+  }) =>
+      _api.create(
+          title: title, description: description, goal: goal, color: color);
+  Future<Project> update(int id, Map<String, dynamic> fields) =>
+      _api.update(id, fields);
+  Future<void> delete(int id) => _api.delete(id);
+}

lib/data/repositories/tasks_repository.dart

@@ -14,6 +14,7 @@ class TasksRepository {
     required TaskStatus status,
     required TaskPriority priority,
     DateTime? dueDate,
+    int? projectId,
   }) =>
       _api.create(
         title: title,
@@ -21,6 +22,7 @@ class TasksRepository {
         status: status,
         priority: priority,
         dueDate: dueDate,
+        projectId: projectId,
       );
 
   Future<Task> update(int id, Map<String, dynamic> fields) =>