紧急修复：为 nav-right 添加 flex-shrink 和 min-height 防止高度坍塌

问题根源：
- 虽然设置了 align-items: stretch 和 height: 100%，但 nav-right 仍被计算为 0px
- 原因是 flex 容器中的 nav-right 被隐式设置为 flex-shrink: 1（默认值），导致在计算时被压缩
- 同时缺少 min-height 导致可能的进一步坍塌

关键修复属性：
- flex-shrink: 0 - 防止 flex 项在 nav-header 中被压缩
- min-height: 50px/48px/44px - 设置明确的最小高度作为备份（对应各断点的 nav-header 高度）

修改范围：
767px 断点（common.css + index.css）:
  - .nav-header .nav-right 添加 flex-shrink: 0; min-height: 50px;
  - .nav-right 添加 flex-shrink: 0; min-height: 50px;

575px 断点（common.css + index.css）:
  - 同上，但 min-height: 48px

360px 断点（index.css）:
  - 同上，但 min-height: 44px

基础规则保持不变

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

common/common.css

@@ -1295,24 +1295,29 @@
     padding: 0 12px;
     display: flex !important;
     align-items: stretch !important;
+    justify-content: space-between !important;
   }
 
   .nav-header .nav-left {
     display: flex !important;
     align-items: stretch !important;
-    flex: 1;
+    flex: 0 1 auto;
   }
 
   .nav-header .nav-right {
     display: flex !important;
     align-items: stretch !important;
     height: 100% !important;
+    flex-shrink: 0;
+    min-height: 50px;
   }
 
   .nav-right {
     display: flex !important;
     align-items: stretch !important;
     height: 100% !important;
+    flex-shrink: 0;
+    min-height: 50px;
   }
 
   .nav-header .nav-left .nav-icon img {
@@ -1513,24 +1518,29 @@
     padding: 0 10px;
     display: flex !important;
     align-items: stretch !important;
+    justify-content: space-between !important;
   }
 
   .nav-header .nav-left {
     display: flex !important;
     align-items: stretch !important;
-    flex: 1;
+    flex: 0 1 auto;
   }
 
   .nav-header .nav-right {
     display: flex !important;
     align-items: stretch !important;
     height: 100% !important;
+    flex-shrink: 0;
+    min-height: 48px;
   }
 
   .nav-right {
     display: flex !important;
     align-items: stretch !important;
     height: 100% !important;
+    flex-shrink: 0;
+    min-height: 48px;
   }
 
   .nav-header .nav-left .nav-icon img {