fix(workflow): add reasoning content, suggested questions, citations and audio status support

- Introduce `reasoning_content`, `suggested_questions`, `citations`, and `audio_status` fields in conversation and app response schemas
- Conditionally set `audio_status` to `"pending"` only when `audio_url` is present
- Replace `model_dump` override with `@model_serializer(mode="wrap")` for cleaner serialization logic
- Change knowledge base validation failure from `RuntimeError` to warning + `continue` to avoid halting retrieval on invalid KB

api/app/services/draft_run_service.py

@@ -754,7 +754,7 @@ class AgentRunService:
                 ) if not sub_agent else [],
                 "citations": filtered_citations,
                 "audio_url": audio_url,
-                "audio_status": "pending"
+                "audio_status": "pending" if audio_url else None
             }
 
             logger.info(