feat: 新增全局确认弹窗、多页面UI优化与网络日志开关

1.  新增全局二次确认弹窗组件confirm_box，支持自定义参数并对标小程序实现
2.  优化班级板块多处UI：
    - 修复point_rank_view中Web端字体溢出问题，使用FittedBox自适应缩放
    - 重构class_update_widgets的PostCard，新增卡片背景控制开关并替换光晕实现
    - 优化class_update_view的在线同学栏与头像组布局，支持动态计算展示数量
    - 调整my_update_detail_page的评论区结构，修复评论高亮与删除浮层定位问题
3.  为dio_client新增网络日志总开关，可按需开启请求响应打印
4.  修复多处代码格式与注释细节问题

lib/features/class/widgets/class_update_widgets.dart

@@ -1,3 +1,5 @@
+import 'dart:ui' as ui;
+
 import 'package:cached_network_image/cached_network_image.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_screenutil/flutter_screenutil.dart';
@@ -25,6 +27,7 @@ class PostCard extends StatelessWidget {
     required this.onLike,
     required this.onComment,
     this.showCommentComposer = true,
+    this.hasCardBackground = true,
   });
 
   final UserPostDto post;
@@ -34,6 +37,9 @@ class PostCard extends StatelessWidget {
   /// 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;
 
+  /// 是否显示白色卡片背景（列表页 true；详情页与留言区共用一张大卡片 → false）
+  final bool hasCardBackground;
+
   String get _avatar {
     final url = ImgUrl.build(post.avatar);
     return url.isEmpty
@@ -54,6 +60,54 @@ class PostCard extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final card = Stack(
+      children: [
+        Positioned(
+          top: 0,
+          left: 0,
+          right: 0,
+          height: 85.h,
+          child: IgnorePointer(
+            // 卡片顶部右上角光晕，对标 Vue SubjectCard::before 的双层 radial-gradient
+            child: CustomPaint(painter: _CardTopGlowPainter()),
+          ),
+        ),
+        Padding(
+          padding: EdgeInsets.symmetric(horizontal: 16.w, vertical: 21.h),
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [
+              CardHeader(
+                avatar: _avatar,
+                name: _name,
+                subject: _subject,
+                time: _time,
+              ),
+              if (post.type == 1) ...[
+                SizedBox(height: 5.h),
+                ResolveProblemBox(desc: post.content),
+              ],
+              if (post.type == 2 || post.type == 3) ...[
+                SizedBox(height: 15.h),
+                AlbumDesc(text: post.content),
+              ],
+              if (post.urls.isNotEmpty) ...[
+                SizedBox(height: 15.h),
+                AlbumGrid(urls: post.urls.map(ImgUrl.build).toList()),
+              ],
+              SizedBox(height: 10.h),
+              LikeCommentBar(
+                post: post,
+                onLike: onLike,
+                onComment: onComment,
+                showComposer: showCommentComposer,
+              ),
+            ],
+          ),
+        ),
+      ],
+    );
+    if (!hasCardBackground) return card;
     return Container(
       margin: EdgeInsets.only(bottom: 10.h),
       clipBehavior: Clip.antiAlias,
@@ -61,67 +115,65 @@ class PostCard extends StatelessWidget {
         color: Colors.white,
         borderRadius: BorderRadius.circular(15.r),
       ),
-      child: Stack(
-        children: [
-          Positioned(
-            top: 0,
-            left: 0,
-            right: 0,
-            height: 85.h,
-            child: IgnorePointer(
-              child: DecoratedBox(
-                decoration: BoxDecoration(
-                  gradient: LinearGradient(
-                    begin: Alignment.topRight,
-                    end: Alignment.bottomLeft,
-                    colors: [
-                      const Color(0xFFCEE9FF).withValues(alpha: 0.9),
-                      const Color(0xFFF6FBFF).withValues(alpha: 0.0),
-                    ],
-                  ),
-                ),
-              ),
-            ),
-          ),
-          Padding(
-            padding: EdgeInsets.symmetric(horizontal: 16.w, vertical: 21.h),
-            child: Column(
-              crossAxisAlignment: CrossAxisAlignment.start,
-              children: [
-                CardHeader(
-                  avatar: _avatar,
-                  name: _name,
-                  subject: _subject,
-                  time: _time,
-                ),
-                if (post.type == 1) ...[
-                  SizedBox(height: 5.h),
-                  ResolveProblemBox(desc: post.content),
-                ],
-                if (post.type == 2 || post.type == 3) ...[
-                  SizedBox(height: 15.h),
-                  AlbumDesc(text: post.content),
-                ],
-                if (post.urls.isNotEmpty) ...[
-                  SizedBox(height: 15.h),
-                  AlbumGrid(urls: post.urls.map(ImgUrl.build).toList()),
-                ],
-                SizedBox(height: 10.h),
-                LikeCommentBar(
-                  post: post,
-                  onLike: onLike,
-                  onComment: onComment,
-                  showComposer: showCommentComposer,
-                ),
-              ],
-            ),
-          ),
-        ],
-      ),
+      child: card,
     );
   }
 }
 
+/// 卡片顶部光晕：对标 Vue `SubjectCard::before` 的两层 radial-gradient
+/// （椭圆均以右上角为圆心，CSS 先写的在上层）：
+///   radial-gradient(120% 85% at 100% 0%,
+///       rgba(206,233,255,1) 0%, rgba(206,233,255,.26) 10%, rgba(255,255,255,0) 58%)
+///   radial-gradient(75% 55% at 100% 0%,
+///       rgba(196,226,255,.88) 0%, rgba(255,255,255,1) 64%)
+class _CardTopGlowPainter extends CustomPainter {
+  @override
+  void paint(Canvas canvas, Size size) {
+    // 先画下层（更小、偏白的光晕），再画上层（更大的浅蓝光晕）
+    _paintGlow(
+      canvas,
+      size,
+      rx: size.width * 0.75,
+      ry: size.height * 0.55,
+      colors: [const Color(0xFFC4E2FF).withValues(alpha: 0.88), Colors.white],
+      stops: const [0, 0.64],
+    );
+    _paintGlow(
+      canvas,
+      size,
+      rx: size.width * 1.20,
+      ry: size.height * 0.85,
+      colors: [
+        const Color(0xFFCEE9FF),
+        const Color(0xFFCEE9FF).withValues(alpha: 0.26),
+        Colors.white.withValues(alpha: 0.0),
+      ],
+      stops: const [0, 0.10, 0.58],
+    );
+  }
+
+  /// 用 canvas.scale 把圆形径向渐变拉成 CSS 的椭圆（圆心 = 右上角）
+  void _paintGlow(
+    Canvas canvas,
+    Size size, {
+    required double rx,
+    required double ry,
+    required List<Color> colors,
+    required List<double> stops,
+  }) {
+    canvas.save();
+    canvas.translate(size.width, 0);
+    canvas.scale(rx, ry);
+    final Paint paint = Paint()
+      ..shader = ui.Gradient.radial(Offset.zero, 1.0, colors, stops);
+    canvas.drawRect(const Rect.fromLTWH(-1, 0, 1, 1), paint);
+    canvas.restore();
+  }
+
+  @override
+  bool shouldRepaint(covariant CustomPainter oldDelegate) => false;
+}
+
 /// 卡片标题：头像 + 姓名 + 学科标签 + 时间
 class CardHeader extends StatelessWidget {
   const CardHeader({