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/providers/tasks_provider.dart

@@ -6,6 +6,11 @@ import 'api_client_provider.dart';
 final tasksProvider =
     AsyncNotifierProvider<TasksNotifier, List<Task>>(TasksNotifier.new);
 
+final projectTasksProvider =
+    FutureProvider.family<List<Task>, int>((ref, projectId) {
+  return ref.watch(tasksRepositoryProvider).getByProject(projectId);
+});
+
 class TasksNotifier extends AsyncNotifier<List<Task>> {
   @override
   Future<List<Task>> build() async {