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_modifier_inputs.py

@@ -0,0 +1,54 @@
+import unittest
+from pathlib import Path
+from types import SimpleNamespace
+from common_test_support import load_common_modules
+PROJECT_ROOT=Path(__file__).resolve().parents[1]
+
+class ModifierInputsTest(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.modules = load_common_modules()
+
+    def test_runtime_modifier_enum_input_uses_string_identifier(self):
+        enum_items = (
+            SimpleNamespace(identifier="SURFACE"),
+            SimpleNamespace(identifier="BALLOON"),
+        )
+        value_property = SimpleNamespace(type="ENUM", enum_items=enum_items)
+        input_slot = SimpleNamespace(
+            value=None,
+            bl_rna=SimpleNamespace(properties={"value": value_property}),
+        )
+        modifier = SimpleNamespace(
+            properties=SimpleNamespace(
+                inputs=SimpleNamespace(Shape=input_slot),
+            )
+        )
+
+        self.modules.object.set_modifier_input(modifier, "Shape", 1)
+
+        self.assertEqual(input_slot.value, "BALLOON")
+
+
+    def test_modifier_inputs_support_rna_and_dictionary_values(self):
+        value_property = SimpleNamespace(type="FLOAT")
+        input_slot = SimpleNamespace(
+            value=None,
+            bl_rna=SimpleNamespace(properties={"value": value_property}),
+        )
+        runtime_modifier = SimpleNamespace(
+            properties=SimpleNamespace(
+                inputs=SimpleNamespace(Thickness=input_slot),
+            )
+        )
+
+        self.modules.object.set_modifier_input(runtime_modifier, "Thickness", 2.0)
+
+        self.assertEqual(input_slot.value, 2.0)
+
+        class LegacyModifier(dict):
+            properties = None
+
+        legacy_modifier = LegacyModifier()
+        self.modules.object.set_modifier_input(legacy_modifier, "Shape", 1)
+        self.assertEqual(legacy_modifier["Shape"], 1)