fix: auto-fix code issues (cron)

- 修复重复导入/字段 (llm_client.py 中的重复注释)
- 修复PEP8格式问题 (E501行长度超过100字符)
- 修复多行SQL语句和字符串格式化
- 修复f-string过长问题

涉及文件:
- backend/developer_ecosystem_manager.py
- backend/document_processor.py
- backend/enterprise_manager.py
- backend/export_manager.py
- backend/growth_manager.py
- backend/llm_client.py
- backend/localization_manager.py
- backend/main.py
- backend/neo4j_manager.py
- backend/ops_manager.py
- backend/performance_manager.py
- backend/plugin_manager.py
- backend/search_manager.py
- backend/security_manager.py
- backend/subscription_manager.py
- backend/tenant_manager.py
- backend/test_phase8_task6.py
- backend/test_phase8_task8.py
- backend/tingwu_client.py
- backend/workflow_manager.py

backend/document_processor.py

@@ -75,7 +75,8 @@ class DocumentProcessor:
                 return "\n\n".join(text_parts)
             except ImportError:
                 raise ImportError(
-                    "PDF processing requires PyPDF2 or pdfplumber. Install with: pip install PyPDF2",
+                    "PDF processing requires PyPDF2 or pdfplumber. "
+                    "Install with: pip install PyPDF2",
                 )
         except Exception as e:
             raise ValueError(f"PDF extraction failed: {e!s}")