🐛 修复亮色主题导航栏文字颜色

- 添加 .nav-item 深色文字颜色
- 修复悬停和激活状态的颜色
- 添加 .user-info 深色文字
- 修复用户头像图标颜色

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

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

frontend/app.html

@@ -160,13 +160,27 @@
       border-bottom: 1px solid rgba(102, 126, 234, 0.15);
     }
 
+    body.light-theme .nav-item {
+      color: #1a1a2e;
+    }
+
     body.light-theme .nav-item:hover {
       background: rgba(102, 126, 234, 0.1);
+      color: #5a67d8;
+    }
+
+    body.light-theme .nav-item.active {
+      color: white;
     }
 
     body.light-theme .user-info {
       background: rgba(102, 126, 234, 0.08);
       border-color: rgba(102, 126, 234, 0.2);
+      color: #1a1a2e;
+    }
+
+    body.light-theme .user-info .user-avatar {
+      color: #5a67d8;
     }
 
     /* 亮色主题卡片 */