chore: update tenant admin spec

.kiro/specs/tenant-admin-web/design.md

@@ -186,15 +186,6 @@ async def require_tenant_admin(
     )
 ```
 
-数据隔离通过 `managed_site_ids` 实现：
-
-```python
-def site_filter_clause(admin: CurrentTenantAdmin) -> tuple[str, tuple]:
-    """生成 site_id IN (...) SQL 片段。"""
-    placeholders = ",".join(["%s"] * len(admin.managed_site_ids))
-    return f"site_id IN ({placeholders})", tuple(admin.managed_site_ids)
-```
-
 ### 前端组件结构
 
 ```