fix: auto-fix code issues (cron)

- 修复重复导入/字段
- 修复异常处理 (将裸 except Exception 改为具体异常类型)
- 修复PEP8格式问题
- 清理未使用导入
- 添加 UUID_LENGTH 常量替代魔法数字
- 添加 DEFAULT_RATE_LIMIT, MASTER_KEY_RATE_LIMIT, IP_RATE_LIMIT 常量
- 添加 MAX_TEXT_LENGTH, DEFAULT_TIMEOUT 常量

涉及文件:
- backend/main.py
- backend/db_manager.py
- backend/llm_client.py
- backend/neo4j_manager.py
- backend/tingwu_client.py
- backend/tenant_manager.py
- backend/growth_manager.py
- backend/workflow_manager.py
- backend/image_processor.py
- backend/multimodal_entity_linker.py
- backend/multimodal_processor.py
- backend/plugin_manager.py
- backend/rate_limiter.py

backend/workflow_manager.py

@@ -15,7 +15,6 @@ import hashlib
 import hmac
 import json
 import logging
-import urllib.parse
 import uuid
 from collections.abc import Callable
 from dataclasses import dataclass, field
@@ -29,6 +28,12 @@ from apscheduler.schedulers.asyncio import AsyncIOScheduler
 from apscheduler.triggers.cron import CronTrigger
 from apscheduler.triggers.interval import IntervalTrigger
 
+# Constants
+UUID_LENGTH = 8  # UUID 截断长度
+DEFAULT_TIMEOUT = 300  # 默认超时时间(秒)
+DEFAULT_RETRY_COUNT = 3  # 默认重试次数
+DEFAULT_RETRY_DELAY = 5  # 默认重试延迟(秒)
+
 # Configure logging
 logging.basicConfig(level=logging.INFO)
 logger = logging.getLogger(__name__)
@@ -1073,7 +1078,7 @@ class WorkflowManager:
 
         # 创建工作流执行日志
         log = WorkflowLog(
-            id=str(uuid.uuid4())[:8],
+            id=str(uuid.uuid4())[:UUID_LENGTH],
             workflow_id=workflow_id,
             status=TaskStatus.RUNNING.value,
             start_time=now,
@@ -1200,7 +1205,7 @@ class WorkflowManager:
 
         # 创建任务日志
         task_log = WorkflowLog(
-            id=str(uuid.uuid4())[:8],
+            id=str(uuid.uuid4())[:UUID_LENGTH],
             workflow_id=task.workflow_id,
             task_id=task.id,
             status=TaskStatus.RUNNING.value,