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.

tools/node_assets/validate.py

@@ -18,7 +18,6 @@ from anyimage.common.material import (
 )
 from anyimage.common.node import load_node_group, node_asset_path
 from anyimage.operators.cutout_tool.shape import (
-    CUTOUT_NODE_GROUP_NAME,
     CUTOUT_NODE_GROUP_NAMES,
 )
 
@@ -41,9 +40,8 @@ def main():
     image_layer = load_node_group(IMAGE_MATERIAL_NODE_GROUP_NAME)
     depth_layer = load_node_group(DEPTH_MATERIAL_NODE_GROUP_NAME)
     shadeless = load_node_group("O Shadeless")
-    cutout = load_node_group(CUTOUT_NODE_GROUP_NAME)
     cutout_groups = {
-        name: bpy.data.node_groups[name] for name in CUTOUT_NODE_GROUP_NAMES.values()
+        name: load_node_group(name) for name in set(CUTOUT_NODE_GROUP_NAMES.values())
     }
     expected_names = {
         "O Mesh Plane",
@@ -51,7 +49,6 @@ def main():
         IMAGE_MATERIAL_NODE_GROUP_NAME,
         DEPTH_MATERIAL_NODE_GROUP_NAME,
         "O Shadeless",
-        CUTOUT_NODE_GROUP_NAME,
         *CUTOUT_NODE_GROUP_NAMES.values(),
     }
     with bpy.data.libraries.load(str(node_asset_path()), link=False) as (source, _):
@@ -115,19 +112,10 @@ def main():
     assert shadeless.bl_idname == "ShaderNodeTree"
     assert input_names(shadeless) == ["Color"]
 
-    assert cutout.name == CUTOUT_NODE_GROUP_NAME
-    assert cutout.bl_idname == "GeometryNodeTree"
-    assert cutout.is_modifier
-    assert input_names(cutout)[:4] == [
-        "Geometry",
-        "Shape",
-        "Inward Axis",
-        "Thickness",
-    ]
     assert set(cutout_groups) == set(CUTOUT_NODE_GROUP_NAMES.values())
     for group in cutout_groups.values():
         assert group.bl_idname == "GeometryNodeTree"
-        assert not group.is_modifier
+        assert group.is_modifier
         assert input_names(group)[0] == "Geometry"
 
     public_groups = {
@@ -136,7 +124,7 @@ def main():
         image_layer,
         depth_layer,
         shadeless,
-        cutout,
+        *cutout_groups.values(),
     }
     loaded = {*public_groups, *cutout_groups.values()}
     for group in loaded: