Add cutout shell and volume node assets for depth volume processing

- Implemented `cutout_shell.py` to build front normals and shell positions for balloon geometry.
- Created `cutout_volume.py` to establish smooth center fields and manage balloon surface attributes.
- Introduced `pisa_sr_export.py` for exporting PiSA-SR components with dependencies and asset finalization.

src/anyimage/common/node.py

@@ -10,10 +10,12 @@ def node_asset_path():
     return Path(__file__).resolve().parents[1] / "assets" / NODE_ASSET_NAME
 
 
-def load_node_group(group_name):
+def load_node_group(group_name, *, asset_revision=None):
     existing = bpy.data.node_groups.get(group_name)
     if existing is not None:
-        return existing
+        if asset_revision is None or existing.get("anyimage_asset_revision") == asset_revision:
+            return existing
+        existing.name = group_name + " (Saved)"
 
     asset_path = node_asset_path()
     if not asset_path.is_file():