Project task view: tapping a project shows milestone-grouped task list

- ProjectLibraryCard.onTap navigates to /projects/:id/tasks
- New ProjectTasksScreen: milestone sections with coloured dot,
  done/total counter and thin progress bar; unassigned tasks at bottom
- Status cycle icon updates optimistically (pendingStatus map) so
  the list doesn't flash on every tap; syncs global tasksProvider
- New route /projects/:id/tasks registered in app.dart
- TasksApi.getByProject + TasksRepository + projectTasksProvider (family)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/data/repositories/tasks_repository.dart

@@ -27,6 +27,7 @@ class TasksRepository {
         parentId: parentId,
       );
 
+  Future<List<Task>> getByProject(int projectId) => _api.getByProject(projectId);
   Future<List<Task>> getSubTasks(int parentId) => _api.getSubTasks(parentId);
 
   Future<Task> update(int id, Map<String, dynamic> fields) =>