fix(USD): use canonical SCHAEFFLER material names for USD material bindings

Material prims now use resolved canonical names (e.g.
SCHAEFFLER_010101_Steel_Bare) instead of source object names. When
importing USD in Blender, materials show the correct SCHAEFFLER names
directly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

render-worker/scripts/export_step_to_usd.py

@@ -759,9 +759,15 @@ def main() -> None:
                     )
                     pv_seam.Set(Vt.Vec2iArray([Gf.Vec2i(a, b) for a, b in seam_idx_pairs]))
 
-            # ── Material placeholder + binding ────────────────────────────
-            mat_name = _prim_name(source_name) if source_name else f"mat_{part_key}"
-            mat_usd_path = f"/Root/Looks/{mat_name}"
+            # ── Material binding ──────────────────────────────────────────
+            # Use canonical SCHAEFFLER material name when resolved; fall back
+            # to source_name so Blender imports show meaningful material names
+            # even without the library .blend appended.
+            if canonical_mat:
+                mat_prim_name = _prim_name(canonical_mat)
+            else:
+                mat_prim_name = _prim_name(source_name) if source_name else f"mat_{part_key}"
+            mat_usd_path = f"/Root/Looks/{mat_prim_name}"
             if not stage.GetPrimAtPath(mat_usd_path):
                 UsdShade.Material.Define(stage, mat_usd_path)
             UsdShade.MaterialBindingAPI(mesh.GetPrim()).Bind(