chore: checkpoint current workspace changes

docs/reference/NahidaUnity/README.md

@@ -0,0 +1,21 @@
+# Nahida Unity Reference Snapshot
+
+This directory stores the Unity-side raw reference files that describe how the original Nahida sample is assembled.
+
+Why it lives under `docs/reference/` instead of `project/Assets/`:
+- The engine asset pipeline imports `.mat` as engine-native materials.
+- The engine asset pipeline imports `.shader` as engine-native shaders.
+- These files are Unity formats, not engine-native formats.
+- Keeping them out of `project/Assets` avoids false imports and noisy asset errors.
+
+What is kept here:
+- Unity materials
+- Unity shader and HLSL files
+- Unity runtime helper scripts
+- Unity sample scene
+- Unity URP settings assets
+
+The engine-native migration target remains:
+- `project/Assets/Characters/Nahida/`
+
+Use this folder as semantic reference only while rebuilding the runtime path inside XCEngine.