Phase 23: WebUI separation — api.py + youlbot-webui project

- api.py: /chat SSE done event now includes run_id for feedback linking
  (format: data: {"__done": true, "run_id": "uuid"})
- api.py: Add POST /feedback endpoint with LangSmith integration
- ROADMAP.md: Add Phase 23 documentation

Note: youlbot-webui/ created at /Users/sal/workspace/youlbot-webui/
(separate project, tracked independently)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api.py

@@ -11,8 +11,12 @@
                       json={"message": "안녕", "user_id": "홍길동"},
                       headers=headers, timeout=120) as r:
             for line in r.iter_lines():
-                if line.startswith("data: ") and line != "data: [DONE]":
-                    print(json.loads(line[6:]), end="", flush=True)
+                if not line.startswith("data: "):
+                    continue
+                payload = json.loads(line[6:])
+                if isinstance(payload, dict) and payload.get("__done"):
+                    break  # run_id = payload["run_id"]
+                print(payload, end="", flush=True)
 """
 import json
 import os
@@ -72,6 +76,14 @@ class ChatRequest(BaseModel):
     show_thinking: bool = False
 
 
+class FeedbackRequest(BaseModel):
+    user_id: str = "default"
+    user_msg: str
+    asst_msg: str
+    rating: int
+    run_id: str | None = None
+
+
 # ── 엔드포인트 ────────────────────────────────────────────────
 
 
@@ -88,11 +100,26 @@ async def chat(req: ChatRequest, _=Depends(_auth)):
     async def generate():
         async for token in agent.stream_response(req.message, show_thinking=req.show_thinking):
             yield f"data: {json.dumps(token, ensure_ascii=False)}\n\n"
-        yield "data: [DONE]\n\n"
+        yield f"data: {json.dumps({'__done': True, 'run_id': agent.last_run_id}, ensure_ascii=False)}\n\n"
 
     return StreamingResponse(generate(), media_type="text/event-stream")
 
 
+@app.post("/feedback")
+async def save_feedback(req: FeedbackRequest, _=Depends(_auth)):
+    """👍/👎 피드백 저장. LangSmith 트레이싱 활성화 시 자동 연동."""
+    _container.feedback_repository().save_feedback(
+        req.user_id, req.user_msg, req.asst_msg, req.rating, req.run_id
+    )
+    if req.run_id and os.getenv("LANGCHAIN_TRACING_V2") == "true":
+        try:
+            from langsmith import Client
+            Client().create_feedback(run_id=req.run_id, key="user_feedback", score=req.rating)
+        except Exception:
+            pass
+    return {"saved": True}
+
+
 @app.post("/reset")
 async def reset(user_id: str = "default", _=Depends(_auth)):
     """대화 이력 초기화."""