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/app.dart

@@ -15,6 +15,7 @@ import 'providers/update_provider.dart';
 import 'providers/tasks_provider.dart';
 import 'screens/auth/login_screen.dart';
 import 'screens/briefing/briefing_screen.dart';
+import 'screens/library/project_tasks_screen.dart';
 import 'screens/chat/chat_screen.dart';
 import 'screens/chat/conversations_tab_screen.dart';
 import 'screens/library/library_screen.dart';
@@ -107,6 +108,12 @@ final routerProvider = Provider<GoRouter>((ref) {
           taskId: int.parse(state.pathParameters['id']!),
         ),
       ),
+      GoRoute(
+        path: Routes.projectTasks,
+        builder: (_, state) => ProjectTasksScreen(
+          projectId: int.parse(state.pathParameters['id']!),
+        ),
+      ),
       GoRoute(
         path: Routes.chat,
         builder: (_, state) => ChatScreen(