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) {

lib/data/api/projects_api.dart

@@ -0,0 +1,71 @@
+import 'package:dio/dio.dart';
+
+import '../models/project.dart';
+import 'api_client.dart';
+
+class ProjectsApi {
+  final Dio _dio;
+  const ProjectsApi(this._dio);
+
+  Future<List<Project>> getAll({String? status}) async {
+    try {
+      final response = await _dio.get(
+        '/api/projects',
+        queryParameters: status != null ? {'status': status} : null,
+      );
+      final data = response.data as Map<String, dynamic>;
+      final list = data['projects'] as List<dynamic>;
+      return list
+          .map((e) => Project.fromJson(e as Map<String, dynamic>))
+          .toList();
+    } on DioException catch (e) {
+      throw dioToApp(e);
+    }
+  }
+
+  Future<Project> getOne(int id) async {
+    try {
+      final response = await _dio.get('/api/projects/$id');
+      return Project.fromJson(response.data as Map<String, dynamic>);
+    } on DioException catch (e) {
+      throw dioToApp(e);
+    }
+  }
+
+  Future<Project> create({
+    required String title,
+    String? description,
+    String? goal,
+    String? color,
+  }) async {
+    try {
+      final response = await _dio.post('/api/projects', data: {
+        'title': title,
+        if (description != null && description.isNotEmpty)
+          'description': description,
+        if (goal != null && goal.isNotEmpty) 'goal': goal,
+        if (color != null) 'color': color,
+      });
+      return Project.fromJson(response.data as Map<String, dynamic>);
+    } on DioException catch (e) {
+      throw dioToApp(e);
+    }
+  }
+
+  Future<Project> update(int id, Map<String, dynamic> fields) async {
+    try {
+      final response = await _dio.patch('/api/projects/$id', data: fields);
+      return Project.fromJson(response.data as Map<String, dynamic>);
+    } on DioException catch (e) {
+      throw dioToApp(e);
+    }
+  }
+
+  Future<void> delete(int id) async {
+    try {
+      await _dio.delete('/api/projects/$id');
+    } on DioException catch (e) {
+      throw dioToApp(e);
+    }
+  }
+}

lib/data/api/tasks_api.dart

@@ -33,6 +33,7 @@ class TasksApi {
     required TaskStatus status,
     required TaskPriority priority,
     DateTime? dueDate,
+    int? projectId,
   }) async {
     try {
       final response = await _dio.post('/api/tasks', data: {
@@ -41,6 +42,7 @@ class TasksApi {
         'status': status.value,
         'priority': priority.value,
         'due_date': dueDate?.toIso8601String(),
+        if (projectId != null) 'project_id': projectId,
       });
       return Task.fromJson(response.data as Map<String, dynamic>);
     } on DioException catch (e) {