feat(node_assets): add image plane geometry nodes and validation scripts

- Implemented `image_plane.py` to build the Image Plane Geometry Nodes group with customizable parameters for geometry, subdivide, and thickness.
- Created `image_plane_validation.py` to validate the functionality of the image plane, ensuring correct geometry generation and material assignment.
- Developed `material_layers.py` to construct shader node groups for image materials, including depth and normal handling.
- Authored `plane_layouts.py` to define node arrangements for image geometry assets.
- Introduced `shadeless.py` to create a shadeless shader node group that displays color without scene lighting while preserving shadows and reflections.

tests/test_node_loading.py

@@ -0,0 +1,15 @@
+import unittest
+from pathlib import Path
+from common_test_support import load_common_modules
+PROJECT_ROOT=Path(__file__).resolve().parents[1]
+
+class NodeLoadingTest(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.modules = load_common_modules()
+
+    def test_node_asset_path_resolves_bundled_library(self):
+        self.assertEqual(
+            self.modules.node.node_asset_path(),
+            PROJECT_ROOT / "src" / "anyimage" / "assets" / "O_AnyImage.blend",
+        )