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

src/lib/image-workspace.ts

@@ -12,6 +12,7 @@ import {
   designAssetDownloadPath,
   type DesignAsset,
   type DesignAssetSaveResult,
+  type DesignConversation,
   type DesignGenerationTask,
   type DesignWorkspace,
   type DesignWorkspaceBootstrap,
@@ -49,6 +50,10 @@ export function createImageWorkspaceTurnId(): string {
   return createClientId('turn');
 }
 
+export function createImageWorkspaceConversationId(): string {
+  return createClientId('conversation');
+}
+
 function getErrorStatus(error: unknown): number {
   if (error instanceof AppError && typeof error.details?.status === 'number') {
     return error.details.status;
@@ -123,15 +128,42 @@ export function fetchImageWorkspaceProject(workspaceId: string): Promise<DesignW
   );
 }
 
+export function createImageWorkspaceConversation(
+  workspaceId: string,
+  title = '新会话',
+  clientConversationId = createImageWorkspaceConversationId(),
+): Promise<DesignConversation> {
+  return requestData(
+    `${IMAGE_WORKSPACE_API_PATH}/workspaces/${encodeURIComponent(workspaceId)}/conversations`,
+    {
+      method: 'POST',
+      body: JSON.stringify({
+        clientConversationId,
+        title: title.trim(),
+      }),
+    },
+  );
+}
+
+export function fetchImageWorkspaceConversation(
+  workspaceId: string,
+  conversationId: string,
+): Promise<DesignConversation> {
+  return requestData(
+    `${IMAGE_WORKSPACE_API_PATH}/workspaces/${encodeURIComponent(workspaceId)}/conversations/${encodeURIComponent(conversationId)}`,
+  );
+}
+
 export function sendImageWorkspaceMessage(
   workspaceId: string,
+  conversationId: string,
   expectedTurnRevision: number,
   message: string,
   clientTurnId = createImageWorkspaceTurnId(),
   attachmentAssetIds: string[] = [],
-): Promise<DesignWorkspace> {
+): Promise<DesignConversation> {
   return requestData(
-    `${IMAGE_WORKSPACE_API_PATH}/workspaces/${encodeURIComponent(workspaceId)}/messages`,
+    `${IMAGE_WORKSPACE_API_PATH}/workspaces/${encodeURIComponent(workspaceId)}/conversations/${encodeURIComponent(conversationId)}/messages`,
     {
       method: 'POST',
       body: JSON.stringify({
@@ -146,12 +178,13 @@ export function sendImageWorkspaceMessage(
 
 export function confirmImageWorkspaceGeneration(
   workspaceId: string,
+  conversationId: string,
   expectedTurnRevision: number,
   quoteId: string,
   clientTurnId = createImageWorkspaceTurnId(),
-): Promise<DesignWorkspace> {
+): Promise<DesignConversation> {
   return requestData(
-    `${IMAGE_WORKSPACE_API_PATH}/workspaces/${encodeURIComponent(workspaceId)}/quotes/${encodeURIComponent(quoteId)}/confirm`,
+    `${IMAGE_WORKSPACE_API_PATH}/workspaces/${encodeURIComponent(workspaceId)}/conversations/${encodeURIComponent(conversationId)}/quotes/${encodeURIComponent(quoteId)}/confirm`,
     {
       method: 'POST',
       body: JSON.stringify({
@@ -170,10 +203,13 @@ export function fetchImageWorkspaceTasks(
   );
 }
 
-export async function openImageWorkspaceTaskEvents(workspaceId: string): Promise<EventSource> {
+export async function openImageWorkspaceTaskEvents(
+  workspaceId: string,
+  conversationId: string,
+): Promise<EventSource> {
   await ensureHostApiToken();
   return createHostEventSource(
-    `${IMAGE_WORKSPACE_API_PATH}/workspaces/${encodeURIComponent(workspaceId)}/events`,
+    `${IMAGE_WORKSPACE_API_PATH}/workspaces/${encodeURIComponent(workspaceId)}/conversations/${encodeURIComponent(conversationId)}/events`,
   );
 }