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>

offline-backend-20260512/backend/app/gateway/routers/skills.py

@@ -236,7 +236,7 @@ async def _attach_and_filter_tags(
     tag_store: TagStore,
     responses: list[SkillResponse],
     search: str | None,
-    tag_id: str | None,
+    tag_ids: list[str] | None,
 ) -> list[SkillResponse]:
     """Bulk-attach tags to skill responses, then apply name/tag filters."""
     assignments = await tag_store.list_assignments("skill", [r.name for r in responses])
@@ -245,8 +245,9 @@ async def _attach_and_filter_tags(
     if search:
         needle = search.strip().lower()
         responses = [r for r in responses if needle in r.name.lower()]
-    if tag_id:
-        responses = [r for r in responses if any(t.get("id") == tag_id for t in r.tags)]
+    if tag_ids:
+        wanted = set(tag_ids)
+        responses = [r for r in responses if any(t.get("id") in wanted for t in r.tags)]
     return responses
 
 
@@ -262,7 +263,7 @@ async def list_skills(
     skill_store: SkillStore = Depends(get_skill_store),
     tag_store: TagStore = Depends(get_tag_store),
     search: str | None = Query(default=None, description="Case-insensitive fuzzy match on skill name"),
-    tag_id: str | None = Query(default=None, description="Keep only skills carrying this tag"),
+    tag_ids: list[str] | None = Query(default=None, description="Keep skills carrying any of these tags (OR)"),
 ) -> SkillsListResponse:
     try:
         user_id = _current_user_id(request)
@@ -281,7 +282,7 @@ async def list_skills(
             if record is None:
                 continue
             responses.append(_skill_to_response(skill, record))
-        responses = await _attach_and_filter_tags(tag_store, responses, search, tag_id)
+        responses = await _attach_and_filter_tags(tag_store, responses, search, tag_ids)
         return SkillsListResponse(skills=responses)
     except Exception as e:
         logger.error(f"Failed to load skills: {e}", exc_info=True)