refactor: replace print() with structured logging across backend

Replace all print()/stderr logging with Python logging module using
logger = logging.getLogger(__name__) pattern for consistent log levels
and formatting. Extract score conversion to shared score_utils module.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/services/knowledge_base_service.py

@@ -1,6 +1,7 @@
 """
 知识库管理服务
 """
+import logging
 import os
 import hashlib
 from pathlib import Path
@@ -15,6 +16,8 @@ from ..models.user import User
 from ..core.config import get_settings
 from .document_service import DocumentService
 
+logger = logging.getLogger(__name__)
+
 settings = get_settings()
 
 
@@ -106,7 +109,7 @@ class KnowledgeBaseService:
                 existing.user_id = admin.id
             self.db.commit()
             self.db.refresh(existing)
-            print(f"[KB] 升级为系统知识库: {name} (id={existing.id})")
+            logger.info(f"升级为系统知识库: {name} (id={existing.id})")
             return existing.id
 
         # 找到 admin 用户（或任意 superuser）作为 owner
@@ -123,7 +126,7 @@ class KnowledgeBaseService:
         self.db.add(kb)
         self.db.commit()
         self.db.refresh(kb)
-        print(f"[KB] 自动创建系统知识库: {name} (id={kb.id})")
+        logger.info(f"自动创建系统知识库: {name} (id={kb.id})")
         return kb.id
 
     def _resolve_knowledge_base(self, file_path: Path) -> Optional[int]:
@@ -249,13 +252,13 @@ class KnowledgeBaseService:
                         loop.run_until_complete(self.document_service.process_document(document.id))
                         loop.close()
                     except Exception as e:
-                        print(f"后台处理文档 {document.id} 失败: {e}")
+                        logger.error(f"后台处理文档 {document.id} 失败: {e}")
 
                 thread = threading.Thread(target=process_in_background, daemon=True)
                 thread.start()
             except Exception as e:
-                print(f"启动文档处理线程失败: {e}")
-            
+                logger.error(f"启动文档处理线程失败: {e}")
+
             return {"status": "new", "document_id": document.id, "message": "文档创建成功，正在处理中"}
                 
         except Exception as e:
@@ -287,13 +290,13 @@ class KnowledgeBaseService:
                         loop.run_until_complete(self.document_service.process_document(document.id))
                         loop.close()
                     except Exception as e:
-                        print(f"后台处理文档 {document.id} 失败: {e}")
+                        logger.error(f"后台处理文档 {document.id} 失败: {e}")
 
                 thread = threading.Thread(target=process_in_background, daemon=True)
                 thread.start()
             except Exception as e:
-                print(f"启动文档处理线程失败: {e}")
-            
+                logger.error(f"启动文档处理线程失败: {e}")
+
             return {"status": "updated", "document_id": document.id, "message": "文档更新成功，正在重新处理中"}
                 
         except Exception as e:
@@ -482,7 +485,7 @@ class KnowledgeBaseService:
         all_files = [f for f in directory.rglob("*") if f.is_file() and self._is_supported_file(f)]
         total_files = len(all_files)
         
-        print(f"  找到 {total_files} 个支持的文件，开始处理...")
+        logger.info(f"找到 {total_files} 个支持的文件，开始处理...")
         
         for idx, file_path in enumerate(all_files, 1):
             try:
@@ -506,7 +509,7 @@ class KnowledgeBaseService:
                 # 显示进度（每10个文件或最后一个文件时显示）
                 if idx % 10 == 0 or idx == total_files:
                     percentage = (idx * 100) // total_files if total_files > 0 else 0
-                    print(f"\r  处理进度: {idx}/{total_files} ({percentage}%)", end="", flush=True)
+                    logger.info(f"处理进度: {idx}/{total_files} ({percentage}%)")
                 
                 if existing_doc:
                     # 检查是否需要更新
@@ -549,6 +552,6 @@ class KnowledgeBaseService:
                     "error": str(e)
                 })
         
-        print()  # 换行
+        logger.info("文件处理完成")
         results["success"] = len(results["errors"]) == 0
         return results