feat: 工具/技能调用统计 + 用户活动审计 + 标签多选筛选

- 任务1: 用户管理/定时任务管理移入左下角菜单, 从侧边栏删除原入口
- 任务2: 管理员查看用户问答(读 LangGraph checkpoint)与记忆, 新增 admin_users 路由与审计页
- 任务3: 标签筛选改为顶部多选标签栏(OR), agents/skills/scheduled_tasks 三端
- 任务4: 新增 tool_call_metrics 表 + ToolMetricsMiddleware + tool-metrics 路由,
  工具/技能调用统计并入大模型统计页, 含错误分类
- 技能识别: lead agent 经 read_file 加载 /mnt/skills/<cat>/<name>/SKILL.md 调用技能,
  中间件扫描工具参数里的 skills/{public,custom}/{name}/ 路径还原 skill_name
- 单元测试 tests/test_tool_metrics_middleware.py (18 项全过)
- 附: SQLite->MySQL 切换后清理脚本

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend-web/src/components/workspace/settings/skill-settings-page.tsx

@@ -89,9 +89,9 @@ function SkillSettingsList({ onClose }: { onClose?: () => void }) {
   const [staleSheetOpen, setStaleSheetOpen] = useState(false);
   const [archiveSheetOpen, setArchiveSheetOpen] = useState(false);
   const [search, setSearch] = useState("");
-  const [tagId, setTagId] = useState<string | null>(null);
+  const [tagIds, setTagIds] = useState<string[]>([]);
   // Name + tag filtering is resolved server-side via the /api/skills query.
-  const { skills, isLoading, error } = useSkills({ search, tagId });
+  const { skills, isLoading, error } = useSkills({ search, tagIds });
 
   const storedAuth = useMemo(() => getStoredAuth(), []);
   const currentUserId = storedAuth?.user_id ?? null;
@@ -208,9 +208,8 @@ function SkillSettingsList({ onClose }: { onClose?: () => void }) {
       <TagSearchBar
         targetType="skill"
         onSearchChange={setSearch}
-        tagId={tagId}
-        onTagIdChange={setTagId}
-        className="max-w-xl"
+        tagIds={tagIds}
+        onTagIdsChange={setTagIds}
       />
       {isLoading && (
         <div className="text-muted-foreground text-sm">{t.common.loading}</div>