fix(multimodal): support HTML image tags in document extraction and chat responses

- Replace plain image URLs with `<img src="..." data-url="...">` HTML tags in multimodal and document extractor services
- Propagate citations from workflow end events to client responses
- Update system prompts to instruct LLMs to render images using Markdown `![alt](url)` with strict UUID-preserving URL copying

api/app/controllers/service/app_api_controller.py

@@ -296,7 +296,7 @@ async def chat(
                 }
             )
 
-        # 多 Agent 非流式返回
+        # workflow 非流式返回
         result = await app_chat_service.workflow_chat(
 
             message=payload.message,