feat(admin): Agent 并发 - 后台可调同时对话上限并展示 Agent 服务状态

新增运行策略 agentMaxSessions（默认 30，范围 1-64），保存后同时下发到内嵌进程闸门与独立 yingce-agent 的 /v1/limit，降低上限不会中断已开始的对话。系统性能页展示 Agent 服务健康、进行中/排队数量，并可直接修改上限。

web/src/services/api/auth.ts

@@ -350,6 +350,8 @@ export type RuntimeTaskPolicy = {
     agentStepMaxOutputTokens: number;
     /** 画布 Agent 单步模型调用的秒级墙钟；0 表示沿用文本任务超时。 */
     agentStepTimeoutSeconds: number;
+    /** 同时进行中的画布 Agent 轮次上限。审批等待不占用名额。 */
+    agentMaxSessions: number;
 };
 
 export type RuntimeRequestPolicy = {

web/src/services/api/system-performance.ts

@@ -105,9 +105,23 @@ export type SystemPerformance = {
         cacheGroups: SystemPerformanceCacheGroup[];
         statusMessage?: string;
     };
+    agents: SystemPerformanceAgent[];
     build: { version: string; commit: string; buildTime: string; goVersion: string };
 };
 
+export type SystemPerformanceAgent = {
+    id: string;
+    name: string;
+    mode: "remote" | "embedded";
+    endpoint: string;
+    healthy: boolean;
+    active: number;
+    limit: number;
+    queued: number;
+    configuredLimit: number;
+    statusMessage?: string;
+};
+
 export type RuntimeCacheClearResult = {
     scope: "runtime";
     deletedKeys: number;
@@ -120,6 +134,10 @@ export function getSystemPerformance(signal?: AbortSignal) {
     return http.get<SystemPerformance>("/admin/system-performance", { signal });
 }
 
+export function updateAgentSessionLimit(maxSessions: number) {
+    return http.put<SystemPerformanceAgent>("/admin/system-performance/agent-limit", { maxSessions });
+}
+
 export function clearRuntimeCache() {
     return http.post<RuntimeCacheClearResult>("/admin/system-performance/cache/clear", { scope: "runtime" });
 }