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/plugin_manager.py

@@ -11,7 +11,6 @@ import json
 import os
 import sqlite3
 import time
-import urllib.parse
 import uuid
 from dataclasses import dataclass, field
 from datetime import datetime
@@ -20,6 +19,9 @@ from typing import Any
 
 import httpx
 
+# Constants
+UUID_LENGTH = 8  # UUID 截断长度
+
 # WebDAV 支持
 try:
     import webdav4.client as webdav_client
@@ -318,7 +320,7 @@ class PluginManager:
             )
             config_id = existing["id"]
         else:
-            config_id = str(uuid.uuid4())[:8]
+            config_id = str(uuid.uuid4())[:UUID_LENGTH]
             conn.execute(
                 """INSERT INTO plugin_configs
                    (id, plugin_id, config_key, config_value, is_encrypted, created_at, updated_at)
@@ -400,7 +402,7 @@ class ChromeExtensionHandler:
         expires_days: int = None,
     ) -> ChromeExtensionToken:
         """创建 Chrome 扩展令牌"""
-        token_id = str(uuid.uuid4())[:8]
+        token_id = str(uuid.uuid4())[:UUID_LENGTH]
 
         # 生成随机令牌
         raw_token = f"if_ext_{base64.urlsafe_b64encode(os.urandom(32)).decode('utf-8').rstrip('=')}"
@@ -563,7 +565,7 @@ class ChromeExtensionHandler:
             return {"success": False, "error": "Insufficient permissions"}
 
         # 创建转录记录（将网页作为文档处理）
-        transcript_id = str(uuid.uuid4())[:8]
+        transcript_id = str(uuid.uuid4())[:UUID_LENGTH]
         now = datetime.now().isoformat()
 
         # 构建完整文本
@@ -604,7 +606,7 @@ class BotHandler:
         secret: str = "",
     ) -> BotSession:
         """创建机器人会话"""
-        bot_id = str(uuid.uuid4())[:8]
+        bot_id = str(uuid.uuid4())[:UUID_LENGTH]
         now = datetime.now().isoformat()
 
         conn = self.pm.db.get_conn()
@@ -932,7 +934,7 @@ class WebhookIntegration:
         trigger_events: list[str] = None,
     ) -> WebhookEndpoint:
         """创建 Webhook 端点"""
-        endpoint_id = str(uuid.uuid4())[:8]
+        endpoint_id = str(uuid.uuid4())[:UUID_LENGTH]
         now = datetime.now().isoformat()
 
         conn = self.pm.db.get_conn()
@@ -1155,7 +1157,7 @@ class WebDAVSyncManager:
         sync_interval: int = 3600,
     ) -> WebDAVSync:
         """创建 WebDAV 同步配置"""
-        sync_id = str(uuid.uuid4())[:8]
+        sync_id = str(uuid.uuid4())[:UUID_LENGTH]
         now = datetime.now().isoformat()
 
         conn = self.pm.db.get_conn()