Upload docs/primitive_collision_proxy_spec.md with huggingface_hub

docs/primitive_collision_proxy_spec.md

@@ -174,6 +174,7 @@ Generated MJCF files:
 ```text
 mjcf/primitive_geoms_include.xml       # include inside the target body
 mjcf/primitive_collision_include.xml   # standalone wrapper for preview/convenience
+mjcf/preview_world.xml                 # MuJoCo preview scene with raw visual mesh + collision boxes
 ```
 
 Recommended integration:
@@ -183,6 +184,15 @@ Recommended integration:
 <include file="path/to/mjcf/primitive_geoms_include.xml"/>
 ```
 
+For visual debugging in MuJoCo, open:
+
+```text
+mjcf/preview_world.xml
+```
+
+This preview keeps the original visual mesh in gray and the primitive boxes in red.
+By default, the red collision boxes are hidden. Press `C` in `scripts/open_mujoco_preview.py` to toggle them on and off.
+
 ## Output files
 
 ### `proxy/primitive_collision_proxy.json`