chore(backlog): 记录 g137 完成

.ua/backlog.json

@@ -1459,7 +1459,7 @@
       "motivation": "tokens 里有 [data-theme=dark] 整套令牌，但演示页从未切换过：暗色令牌长期无人验证，页面自有 --page-* 变量也只跟系统偏好、不跟显式主题",
       "acceptance": "演示页头部提供暗色主题开关（写 html[data-theme]，localStorage 记忆，初值跟随系统）；--page-* 变量响应 data-theme，媒体查询只在未显式指定时生效；npm run check 全绿",
       "notes": "自补：演示页完善",
-      "status": "open"
+      "status": "done"
     }
   ]
 }

.ua/iterations.log

@@ -181,3 +181,4 @@
 {"ts":"2026-10-26T15:25:53+08:00","id":"g134","result":"done","commit":"2a9193c","summary":"新增 ua sync-counts 幂等改写三处组件计数，verify 正则覆盖 README 标题「共 N 个」并给修法提示"}
 {"ts":"2026-10-26T15:27:19+08:00","id":"g135","result":"done","commit":"21950d9","summary":"form 新增 columns（1/2/3）复用 grid 铺列，窄屏自动单列、按钮区整行；demo 注册表单改两列"}
 {"ts":"2026-10-26T15:28:20+08:00","id":"g136","result":"done","commit":"f6706c1","summary":"新增 link（站外自动补 ↗ 与 rel=noopener noreferrer 并播报新窗口，muted/disabled 齐全），组件 65→66；sync-counts 首跑改写 3 份文档计数"}
+{"ts":"2026-10-26T15:29:51+08:00","id":"g137","result":"done","commit":"55da08f","summary":"演示页头部加暗色主题开关（data-theme + localStorage 记忆，初值跟随系统），--page-* 变量改为响应显式主题、媒体查询仅兜未指定时"}