chore: 添加虚拟环境到仓库

- 添加 backend_service/venv 虚拟环境
- 包含所有Python依赖包
- 注意：虚拟环境约393MB，包含12655个文件

backend_service/venv/bin/fastapi

@@ -0,0 +1,7 @@
+#!/home/huangfukk/DronePlanning/backend_service/venv/bin/python3
+import sys
+from fastapi.cli import main
+if __name__ == '__main__':
+    if sys.argv[0].endswith('.exe'):
+        sys.argv[0] = sys.argv[0][:-4]
+    sys.exit(main())