fix(ai_writing): 笔记来源素材使用真实检索分数并打印请求日志

- 笔记 chunk 的 relevance_score 改用接口返回的 score 字段（向量相似度/RRF），接口无分数时降级为位置估算
- _search_notebook 增加 INFO 级日志，输出每次请求的 payload 和响应 status/body，便于调试

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

offline-backend-20260512/backend/packages/harness/deerflow/agents/ai_writing/nodes/researcher.py

@@ -142,13 +142,15 @@ async def _search_notebook(
                             if not chunk_content:
                                 continue
                             mat_idx += 1
+                            raw_score = chunk.get("score")
+                            chunk_score = float(raw_score) if raw_score is not None else max(0.5, 0.95 - (mat_idx - 1) * 0.03)
                             results.append(Material(
                                 id=f"nb{mat_idx:03d}",
                                 title=doc_title,
                                 content=chunk_content[:500],
                                 source=f"笔记·{doc_title}",
                                 source_type="notebook",
-                                relevance_score=1.0,
+                                relevance_score=chunk_score,
                                 url=doc_url,
                             ))
                 except Exception as e: