fix: 统一AI生成失败提示

core/frontend/src/api.ts

@@ -389,7 +389,8 @@ export const api = {
     return request<{
       running: boolean;
       status: string;
-      error: string;
+      error?: unknown;
+      error_message: string;
       entities: Array<{ id: string; type: "character" | "scene"; name: string; visual_prompt: string; ref_index: number }>;
     }>(`/api/projects/${projectId}/extract-status/`);
   },
@@ -730,7 +731,7 @@ export const api = {
     return request<{ conversation_id: string; tasks: ImageConversationTask[] }>(`/api/ai/image-conversations/${id}/tasks/`);
   },
   generateImageStatus(ids: string[]) {
-    return request<{ tasks: { id: string; status: string; error_message: string; assets: Asset[] }[] }>(`/api/ai/generate-image/?ids=${encodeURIComponent(ids.join(","))}`);
+    return request<{ tasks: { id: string; status: string; error?: unknown; error_message: string; assets: Asset[] }[] }>(`/api/ai/generate-image/?ids=${encodeURIComponent(ids.join(","))}`);
   },
   // —— 自由创作·视频生成 ——
   // 提交秒回(火山 create 同步、慢轮询交给 worker 兜底 + 前端主动 poll);校验失败 400 带中文 detail。