fix(ai): 平台套图改走商品主图参考 image_edit · 模特上身图锁商品+模特双图

- 平台套图(cover)以前纯文生图,不参考真实商品主图 → 出图与商品对不上;
  现以商品主图为参考图1走 image_edit,锁包装一致性,有模特则参考图2=模特
- 新增 build_platform_cover_prompt_refs;model_url 解析对 cover 模式同样生效
- 补回归测试:cover 传商品主图、model 传商品主图+模特图、无主图回落文生图

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

core/backend/apps/ai/views.py

@@ -31,9 +31,11 @@ class GenerateImageView(APIView):
             count = 1
         product_id = str(request.data.get("product_id") or "").strip() or None
         reference_product = bool(request.data.get("reference_product"))
+        model_id = str(request.data.get("model_id") or "").strip() or None
+        ratio = str(request.data.get("ratio") or "").strip() or None
         team = get_current_team(request.user)
         try:
-            tasks = enqueue_standalone_images(team=team, user=request.user, prompt=prompt, mode=mode, count=count, product_id=product_id, reference_product=reference_product)
+            tasks = enqueue_standalone_images(team=team, user=request.user, prompt=prompt, mode=mode, count=count, product_id=product_id, reference_product=reference_product, model_id=model_id, ratio=ratio)
         except ValueError as exc:  # 无可用模型 / 余额不足等,立即反馈
             return Response({"detail": str(exc)}, status=status.HTTP_400_BAD_REQUEST)
         return Response(