fix: support site resources from legacy docker updater

app/application/site/__init__.py

@@ -1 +1,25 @@
 """站点目录、认证与索引资源的应用能力包。"""
+
+from importlib.machinery import EXTENSION_SUFFIXES
+from pathlib import Path
+
+
+def _include_legacy_resource_directory(
+        package_paths: list[str], package_dir: Path
+) -> None:
+    """canonical 扩展缺失时允许读取旧 Docker 更新器写入的资源目录。"""
+    extension_names = tuple(f"sites{suffix}" for suffix in EXTENSION_SUFFIXES)
+    if any((package_dir / name).is_file() for name in extension_names):
+        return
+
+    legacy_dir = package_dir.parent.parent / "helper"
+    if (
+            legacy_dir.is_dir()
+            and any((legacy_dir / name).is_file() for name in extension_names)
+            and str(legacy_dir) not in package_paths
+    ):
+        # 旧镜像内固化的 mp_update.sh 无法随源码热更新，只在过渡场景扩展包搜索路径。
+        package_paths.append(str(legacy_dir))
+
+
+_include_legacy_resource_directory(__path__, Path(__file__).resolve().parent)