chore(backlog): 记录 g339 完成

.ua/backlog.json

@@ -3444,7 +3444,7 @@
       "title": "tooltip 指向箭头",
       "motivation": "tooltip 气泡没有箭头，与触发件的指向关系全靠位置猜，四个方向容易读偏",
       "acceptance": "四方向各有一个与气泡同色的 45° 菱形箭头，全部用 --ua-* 令牌与百分比定位，audit:visual 棘轮零新增字面量",
-      "status": "open",
+      "status": "done",
       "notes": ""
     }
   ]

.ua/iterations.log

@@ -383,3 +383,4 @@
 {"ts":"2026-10-27T02:10:09+08:00","id":"g336","result":"done","commit":"da09e29","summary":"全选框与行复选框补可访问名（选择第 N 行），选中行加 aria-selected；文件仍 198 行"}
 {"ts":"2026-10-27T02:13:15+08:00","id":"g337","result":"done","commit":"1d25c8a","summary":"新增可访问名门禁：verify 扫描 combobox/slider/range 控件，补齐 commandPalette 搜索框 aria-label"}
 {"ts":"2026-10-27T02:14:56+08:00","id":"g338","result":"done","commit":"28972a0","summary":"toast 容器补 aria-live=polite 兜底播报，error 级别 role=alert 抢占"}
+{"ts":"2026-10-27T02:17:29+08:00","id":"g339","result":"done","commit":"e5943aa","summary":"四方向 45° 菱形箭头继承气泡底色，全令牌零新增字面量"}