feat: 统一 AI 设计 Workspace 与生成任务链路

需求：以设计项目组织固定设计 Agent 对话、方向确认和图片视频任务。

实现：新增 Works Square 云端适配与开发态本地适配，统一 Host API、Quote 确认、任务轮询及私有媒体 Range 代理。

electron/main/index.ts

@@ -70,6 +70,7 @@ import {
   isLocalImageWorkspaceDevelopmentEnabled,
   LocalImageWorkspace,
 } from '../image-workspace/local-workspace';
+import { WorksSquareDesignWorkspace } from '../image-workspace/works-square-workspace';
 
 const WINDOWS_APP_USER_MODEL_ID = 'app.niancode.desktop';
 const isE2EMode = process.env.NIANCODE_E2E === '1';
@@ -393,9 +394,11 @@ async function initialize(): Promise<void> {
   });
   const imageWorkspace = localImageWorkspaceEnabled
     ? new LocalImageWorkspace({ userDataDir: app.getPath('userData') })
-    : undefined;
-  if (imageWorkspace) {
+    : new WorksSquareDesignWorkspace();
+  if (localImageWorkspaceEnabled) {
     logger.info('AI painting workspace is using local development storage');
+  } else {
+    logger.info('AI painting workspace is using the Works Square cloud contract');
   }
 
   // Set application menu