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/lib/python3.13/site-packages/uvloop/handles/fsevent.pxd

@@ -0,0 +1,12 @@
+cdef class UVFSEvent(UVHandle):
+    cdef:
+        object callback
+        bint running
+
+    cdef _init(self, Loop loop, object callback, object context)
+    cdef _close(self)
+    cdef start(self, char* path, int flags)
+    cdef stop(self)
+
+    @staticmethod
+    cdef UVFSEvent new(Loop loop, object callback, object context)