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/screens/tasks/task_edit_screen.dart

@@ -6,6 +6,7 @@ import '../../core/exceptions.dart';
 import '../../data/models/task.dart';
 import '../../providers/api_client_provider.dart';
 import '../../providers/tasks_provider.dart';
+import '../../widgets/project_selector.dart';
 
 class TaskEditScreen extends ConsumerStatefulWidget {
   final int? taskId;
@@ -22,6 +23,7 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
   TaskStatus _status = TaskStatus.todo;
   TaskPriority _priority = TaskPriority.medium;
   DateTime? _dueDate;
+  int? _projectId;
   bool _saving = false;
 
   // Future is created once in initState so FutureBuilder never restarts it.
@@ -49,6 +51,7 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
     _status = task.status;
     _priority = task.priority;
     _dueDate = task.dueDate;
+    _projectId = task.projectId;
   }
 
   Future<void> _save() async {
@@ -64,16 +67,18 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
               status: _status,
               priority: _priority,
               dueDate: _dueDate,
+              projectId: _projectId,
             );
       } else {
         await ref.read(tasksProvider.notifier).updateTask(widget.taskId!, {
           'title': _titleController.text.trim(),
-          'description': _descController.text.trim().isEmpty
+          'body': _descController.text.trim().isEmpty
               ? null
               : _descController.text.trim(),
           'status': _status.value,
           'priority': _priority.value,
           'due_date': _dueDate?.toIso8601String(),
+          'project_id': _projectId,
         });
       }
       if (mounted) context.pop();
@@ -216,6 +221,11 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
                             : null,
                         onTap: _pickDate,
                       ),
+                      const SizedBox(height: 16),
+                      ProjectSelector(
+                        value: _projectId,
+                        onChanged: (id) => setState(() => _projectId = id),
+                      ),
                     ],
                   ),
                 ),