fix: 修复缺失的 BeautifulSoup 导入

Co-authored-by: aider (deepseek/deepseek-v4-pro) <aider@aider.chat>

app.py

@@ -16,6 +16,7 @@ from flask import (
     jsonify,
 )
 from werkzeug.utils import secure_filename
+from bs4 import BeautifulSoup
 
 import config
 from helpers import (