feat(rate-limit): 站点级请求频率限制支持继承与自定义

在站点详情流量限制中配置 limit_req_per_ip；渲染按 effective rate 生成多 limit_req_zone，并以站点+IP 隔离计数。

frontend/lib/services/openflare/types.ts

@@ -233,6 +233,7 @@ export interface ProxyRouteItem {
   limit_conn_per_server: number;
   limit_conn_per_ip: number;
   limit_rate: string;
+  limit_req_per_ip: string;
   cache_enabled: boolean;
   cache_policy: string;
   cache_rules: string;
@@ -269,6 +270,7 @@ export interface ProxyRouteMutationPayload {
   limit_conn_per_server?: number;
   limit_conn_per_ip?: number;
   limit_rate?: string;
+  limit_req_per_ip?: string;
   cache_enabled: boolean;
   cache_policy: string;
   cache_rules: string[];