feat: 对接设计 Agent Gateway WebSocket

需求：服务端统一 Agent Gateway 将设计任务状态流切换为 WebSocket，客户端需要实时展示生成任务并支持断线恢复。

实现：Electron Main 管理 Session、一次性 Ticket、WebSocket 心跳与游标续传，按关闭码回收会话；Renderer 继续通过本机 Host API 的 SSE 投影接收任务事件，并保留 REST 降级同步。

验证：typecheck、变更文件 ESLint、37 个聚焦测试及 build:vite 通过。

electron/utils/store.ts

@@ -4,6 +4,7 @@
  */
 
 import { app } from 'electron';
+import { randomUUID } from 'node:crypto';
 import { resolveSupportedLanguage } from '../../shared/language';
 
 // Lazy-load electron-store (ESM module)
@@ -21,6 +22,7 @@ export interface AppSettings {
   launchAtStartup: boolean;
   telemetryEnabled: boolean;
   machineId: string;
+  agentGatewaySessionClientIds: Record<string, string>;
   hasReportedInstall: boolean;
 
   proxyEnabled: boolean;
@@ -68,6 +70,7 @@ function createDefaultSettings(): AppSettings {
     launchAtStartup: false,
     telemetryEnabled: true,
     machineId: '',
+    agentGatewaySessionClientIds: {},
     hasReportedInstall: false,
 
     proxyEnabled: false,
@@ -127,6 +130,39 @@ export async function setSetting<K extends keyof AppSettings>(
   store.set(key, value);
 }
 
+let agentGatewaySessionIdMutation: Promise<void> = Promise.resolve();
+
+async function mutateAgentGatewaySessionClientIds<T>(
+  mutation: (current: Record<string, string>) => Promise<T> | T,
+): Promise<T> {
+  const result = agentGatewaySessionIdMutation.then(async () => {
+    const current = await getSetting('agentGatewaySessionClientIds');
+    return await mutation({ ...current });
+  });
+  agentGatewaySessionIdMutation = result.then(() => undefined, () => undefined);
+  return await result;
+}
+
+export function getOrCreateAgentGatewaySessionClientId(workspaceId: string): Promise<string> {
+  return mutateAgentGatewaySessionClientIds(async (current) => {
+    const existing = current[workspaceId]?.trim();
+    if (existing) return existing;
+    const created = `design-stream-${randomUUID()}`;
+    current[workspaceId] = created;
+    await setSetting('agentGatewaySessionClientIds', current);
+    return created;
+  });
+}
+
+export function rotateAgentGatewaySessionClientId(workspaceId: string): Promise<string> {
+  return mutateAgentGatewaySessionClientIds(async (current) => {
+    const created = `design-stream-${randomUUID()}`;
+    current[workspaceId] = created;
+    await setSetting('agentGatewaySessionClientIds', current);
+    return created;
+  });
+}
+
 /**
  * Get all settings
  */