feat: 支持 AI 设计项目多会话交互

需求：用户可在同一设计项目中新建和切换会话，任务列表保持项目级共享。

实现：
- 增加会话选择、新建入口及本地数据迁移
- Conversation 独立消息、Brief、Quote 与流式状态
- 保留项目任务并修复 Task revision 与 ABA 异步竞态
- 保持 Enter 发送、Shift+Enter 换行及 IME 保护

tests/unit/image-workspace-api.test.ts

@@ -59,11 +59,11 @@ describe('AI design renderer API boundary', () => {
   });
 
   it('opens task events only after the local Host API token is ready', async () => {
-    const source = await openImageWorkspaceTaskEvents('workspace/one');
+    const source = await openImageWorkspaceTaskEvents('workspace/one', 'conversation/one');
 
     expect(source).toBe(createHostEventSourceMock.mock.results[0].value);
     expect(createHostEventSourceMock).toHaveBeenCalledWith(
-      '/api/works/image-workspace/workspaces/workspace%2Fone/events',
+      '/api/works/image-workspace/workspaces/workspace%2Fone/conversations/conversation%2Fone/events',
     );
     expect(ensureHostApiTokenMock.mock.invocationCallOrder[0])
       .toBeLessThan(createHostEventSourceMock.mock.invocationCallOrder[0]);
@@ -84,13 +84,14 @@ describe('AI design renderer API boundary', () => {
   it('sends conversation turns with the current turn revision and no provider settings', async () => {
     await sendImageWorkspaceMessage(
       'workspace/one',
+      'conversation/one',
       4,
       '  继续调整构图  ',
       'turn-client-1',
     );
 
     const [path, init] = hostApiFetchMock.mock.calls[0];
-    expect(path).toBe('/api/works/image-workspace/workspaces/workspace%2Fone/messages');
+    expect(path).toBe('/api/works/image-workspace/workspaces/workspace%2Fone/conversations/conversation%2Fone/messages');
     expect(init).toMatchObject({ method: 'POST' });
     expect(JSON.parse(String(init?.body))).toMatchObject({
       expectedTurnRevision: 4,
@@ -104,6 +105,7 @@ describe('AI design renderer API boundary', () => {
   it('sends the selected first-frame Asset id with the conversation turn', async () => {
     await sendImageWorkspaceMessage(
       'workspace-one',
+      'conversation-one',
       5,
       '使用作品图片作为视频首帧',
       'turn-first-frame',
@@ -148,11 +150,11 @@ describe('AI design renderer API boundary', () => {
   });
 
   it('confirms a Quote through a separate structured action route', async () => {
-    await confirmImageWorkspaceGeneration('workspace-one', 5, 'quote/one');
+    await confirmImageWorkspaceGeneration('workspace-one', 'conversation-one', 5, 'quote/one');
 
     const [path, init] = hostApiFetchMock.mock.calls[0];
     expect(path).toBe(
-      '/api/works/image-workspace/workspaces/workspace-one/quotes/quote%2Fone/confirm',
+      '/api/works/image-workspace/workspaces/workspace-one/conversations/conversation-one/quotes/quote%2Fone/confirm',
     );
     expect(JSON.parse(String(init?.body))).toMatchObject({
       expectedTurnRevision: 5,