fix(deploy): 后端 requirements.txt 补充 requests 依赖

容器化部署时发现缺少 requests 库导致后端启动失败
Co-Authored-By: Claude <noreply@anthropic.com>

backend/requirements.txt

@@ -6,3 +6,4 @@ pydantic==2.5.3
 python-multipart==0.0.6
 playwright==1.40.0
 websockets==12.0
+requests==2.31.0
\ No newline at end of file