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_docs_command.py

@@ -0,0 +1,42 @@
+import importlib.util
+from pathlib import Path
+
+
+SCRIPT_PATH = Path(__file__).resolve().parents[1] / "tools" / "docs.py"
+SPEC = importlib.util.spec_from_file_location("docs_script", SCRIPT_PATH)
+docs = importlib.util.module_from_spec(SPEC)
+SPEC.loader.exec_module(docs)
+
+
+def test_documentation_command_deploys_project_version(monkeypatch):
+    monkeypatch.setattr(docs, "project_version", lambda: "1.2.3")
+
+    assert docs.documentation_command() == [
+        "mike",
+        "deploy",
+        "--update-aliases",
+        "1.2.3",
+        "latest",
+    ]
+
+
+def test_documentation_command_previews_current_source():
+    assert docs.documentation_command(dev=True) == ["mkdocs", "serve"]
+
+
+def test_main_runs_from_project_root(monkeypatch):
+    calls = []
+    monkeypatch.setattr(
+        docs.subprocess,
+        "run",
+        lambda *args, **kwargs: calls.append((args, kwargs)),
+    )
+
+    docs.main(["-dev"])
+
+    assert calls == [
+        (
+            (["mkdocs", "serve"],),
+            {"cwd": docs.PROJECT_ROOT, "check": True},
+        )
+    ]