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/widgets/library_item_card.dart

@@ -210,7 +210,8 @@ class ProjectLibraryCard extends StatelessWidget {
       margin: const EdgeInsets.symmetric(horizontal: 12, vertical: 4),
       clipBehavior: Clip.antiAlias,
       child: InkWell(
-        onTap: () {}, // No project detail screen in this app
+        onTap: () => context
+            .push('/projects/${project.id}/tasks'),
         borderRadius: BorderRadius.circular(14),
         child: Row(
           children: [