feat(agent): 聊天提交统一走 POST /agent/runs 异步网关

引入 Agent Run 网关替代直连 /sessions/:id/reply，并在 api_lockdown 白名单中放行新入口，避免策略拦截导致聊天不可用。

Co-authored-by: Cursor <cursoragent@cursor.com>

policies.mjs

@@ -205,6 +205,8 @@ const USER_API_ALLOWLIST = [
   { method: 'GET', pattern: /^\/status$/ },
   { method: 'POST', pattern: /^\/agent\/start$/ },
   { method: 'POST', pattern: /^\/agent\/resume$/ },
+  { method: 'POST', pattern: /^\/agent\/runs$/ },
+  { method: 'GET', pattern: /^\/agent\/runs\/[^/]+$/ },
   { method: 'GET', pattern: /^\/sessions$/ },
   { method: 'GET', pattern: /^\/sessions\/[^/]+$/ },
   { method: 'DELETE', pattern: /^\/sessions\/[^/]+$/ },