feat: 完成班级模块全量功能迭代

本次提交完成了班级模块的多项核心功能开发与优化：
1. 新增DELETE请求封装，支持业务删除接口且不自动重试
2. 完善UserPostCommonDto模型，新增头像字段适配详情接口
3. 重构路由架构，使用StatefulShellRoute实现Tab页面保活
4. 新增我的互动页面，包含我的动态/点赞/留言三个子页
5. 新增全部同学页面，展示班级全员信息与在线状态
6. 新增动态详情页面，支持查看完整评论与点赞头像
7. 抽离通用PostListBody组件，复用列表分页与交互逻辑
8. 优化班级列表页加载逻辑与图片预览交互
9. 新增评论删除、多图预览等细节交互功能

lib/features/class/widgets/class_update_widgets.dart

@@ -2,6 +2,7 @@ import 'package:cached_network_image/cached_network_image.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_screenutil/flutter_screenutil.dart';
 import 'package:new_learn/core/api/class/model.dart';
+import 'package:new_learn/core/components/image_preview_viewer.dart';
 import 'package:new_learn/core/components/user_circle_avatar.dart';
 import 'package:new_learn/core/utils/img_url.dart';
 
@@ -23,12 +24,16 @@ class PostCard extends StatelessWidget {
     required this.post,
     required this.onLike,
     required this.onComment,
+    this.showCommentComposer = true,
   });
 
   final UserPostDto post;
   final VoidCallback onLike;
   final ValueChanged<String> onComment;
 
+  /// 是否显示卡片内嵌的评论预览 + 输入框（列表页 true；详情页由全量留言接管）
+  final bool showCommentComposer;
+
   String get _avatar {
     final url = ImgUrl.build(post.avatar);
     return url.isEmpty
@@ -106,6 +111,7 @@ class PostCard extends StatelessWidget {
                   post: post,
                   onLike: onLike,
                   onComment: onComment,
+                  showComposer: showCommentComposer,
                 ),
               ],
             ),
@@ -295,11 +301,26 @@ class AlbumGrid extends StatelessWidget {
       runSpacing: 9.h,
       children: [
         for (int i = 0; i < displayed.length; i++)
-          _gridItem(displayed[i], i, urls.length),
+          GestureDetector(
+            onTap: () => _preview(context, urls, i),
+            child: _gridItem(displayed[i], i, urls.length),
+          ),
       ],
     );
   }
 
+  /// 点击相册图：进入整组大图预览，定位到点中的那张
+  void _preview(BuildContext context, List<String> allUrls, int index) {
+    ImagePreviewViewer.show(
+      context,
+      items: [
+        for (final u in allUrls)
+          PreviewImageItem(imageProvider: CachedNetworkImageProvider(u)),
+      ],
+      initialIndex: index,
+    );
+  }
+
   Widget _gridItem(String url, int index, int total) {
     final more = total > 9 && index == 8 ? total - 9 : 0;
     return ClipRRect(
@@ -344,12 +365,16 @@ class LikeCommentBar extends StatelessWidget {
     required this.post,
     required this.onLike,
     required this.onComment,
+    this.showComposer = true,
   });
 
   final UserPostDto post;
   final VoidCallback onLike;
   final ValueChanged<String> onComment;
 
+  /// 是否显示评论预览 + 输入框（列表页 true；详情页 false，由全量留言列表接管）
+  final bool showComposer;
+
   @override
   Widget build(BuildContext context) {
     return Column(
@@ -370,12 +395,14 @@ class LikeCommentBar extends StatelessWidget {
             MetaButton(icon: Icons.chat_bubble_outline, count: post.replyCount),
           ],
         ),
-        if (post.commons.isNotEmpty) ...[
+        if (showComposer) ...[
+          if (post.commons.isNotEmpty) ...[
+            SizedBox(height: 12.h),
+            CommentPreview(post: post),
+          ],
           SizedBox(height: 12.h),
-          CommentPreview(post: post),
+          CommentInput(onSubmit: onComment),
         ],
-        SizedBox(height: 12.h),
-        CommentInput(onSubmit: onComment),
       ],
     );
   }
@@ -517,20 +544,25 @@ class _CommentInputState extends State<CommentInput> {
   @override
   Widget build(BuildContext context) {
     return Row(
+      crossAxisAlignment: CrossAxisAlignment.end,
       children: [
         Expanded(
           child: Container(
-            height: 30.h,
-            padding: EdgeInsets.symmetric(horizontal: 12.w),
-            alignment: Alignment.centerLeft,
+            constraints: BoxConstraints(minHeight: 30.h),
+            padding: EdgeInsets.symmetric(horizontal: 12.w, vertical: 5.h),
             decoration: BoxDecoration(
               color: Colors.white,
               border: Border.all(color: const Color(0xFFE3ECFF)),
               borderRadius: BorderRadius.circular(10.r),
             ),
+            // multiline：键盘右下角为「换行」，可换行写多条评论
             child: TextField(
               controller: _controller,
               style: const TextStyle(fontSize: 12, color: Color(0xFF1D2B47)),
+              keyboardType: TextInputType.multiline,
+              textInputAction: TextInputAction.newline,
+              minLines: 1,
+              maxLines: 4,
               decoration: const InputDecoration(
                 isDense: true,
                 border: InputBorder.none,