refactor: 重构页面路由结构与积分页面UI，优化列表交互体验

1. 重构路由结构：将班级子页移出ShellBranch，解决tabbar遮挡问题
2. 统一修改全局"没有更多了"提示文案为带品牌标识的版本
3. 重构积分排行榜UI，修复切换状态时的布局抖动问题，替换图标为CDN资源
4. 重构我的积分页面：对齐Vue端UI设计，新增展开收起详情功能，优化背景与布局
5. 优化我的互动页面布局与样式，新增背景图支持

lib/core/router/app_router.dart

@@ -95,34 +95,33 @@ final GoRouter appRouter = GoRouter(
             GoRoute(path: '/recite', builder: (_, _) => const RecitePage()),
           ],
         ),
-        // 班级（含班级模块子页：全部同学 / 我的互动 / 动态详情）
+        // 班级（只有主 tab 页在 ShellBranch 内，子页放顶层避免 tabbar 遮挡）
         StatefulShellBranch(
           routes: [
             GoRoute(path: '/class', builder: (_, _) => const ClassPage()),
-            GoRoute(
-              path: '/class/all-student',
-              builder: (_, _) => const AllStudentPage(),
-            ),
-            GoRoute(
-              path: '/class/my-interact',
-              builder: (_, _) => const MyInteractPage(),
-            ),
-            GoRoute(
-              path: '/class/my-update-detail',
-              builder: (_, state) =>
-                  MyUpdateDetailPage(initialPost: state.extra as UserPostDto),
-            ),
           ],
         ),
-        // 我的（含我的积分页）
+        // 我的
         StatefulShellBranch(
-          routes: [
-            GoRoute(path: '/my', builder: (_, _) => const MyPage()),
-            GoRoute(path: '/myPoint', builder: (_, _) => const MyPointPage()),
-          ],
+          routes: [GoRoute(path: '/my', builder: (_, _) => const MyPage())],
         ),
       ],
     ),
+    // ---------- 二级业务页（不在 ShellBranch 内，push 时不显示 tabbar） ----------
+    GoRoute(
+      path: '/class/all-student',
+      builder: (_, _) => const AllStudentPage(),
+    ),
+    GoRoute(
+      path: '/class/my-interact',
+      builder: (_, _) => const MyInteractPage(),
+    ),
+    GoRoute(
+      path: '/class/my-update-detail',
+      builder: (_, state) =>
+          MyUpdateDetailPage(initialPost: state.extra as UserPostDto),
+    ),
+    GoRoute(path: '/myPoint', builder: (_, _) => const MyPointPage()),
     // ---------- 首次启动隐私协议页 ----------
     GoRoute(
       path: '/privacy-consent',