feat(M5-M7): embed canonical material names in USD via customData + pxr direct read

- export_step_to_usd.py: accept --material_map CLI arg, write
  schaeffler:canonicalMaterialName as customData on each Mesh prim,
  fix geometry transform (strip shape Location before face exploration,
  apply both face_loc and shape_loc sequentially)
- import_usd.py: after Blender USD import, use pxr to read customData
  directly from the USD file — builds {part_key: material_name} lookup
  (Blender ignores STRING primvars and customData, but pxr reads both)
- _blender_materials.py: add apply_material_library_direct() for exact
  dict-based material assignment without name-matching heuristics
- _blender_scene_setup.py: prefer direct USD lookup, fall back to
  name-matching for legacy USD files without material metadata
- export_glb.py (generate_usd_master_task): resolve material_map via
  material_service.resolve_material_map() and pass to subprocess;
  include material hash in cache key for invalidation
- ROADMAP.md: update P5 status, add M5-M7 milestones

Tested: 3/3 parts matched (ans_lfs120), 172/175 parts matched
(F-802007.TR4-D1-H122AG). Previous: 0/25 matched.

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

.claude/commands/plan.md

@@ -72,7 +72,7 @@ What is unclear? What could go wrong?
 | Queue | Worker | Concurrency | Use for |
 |---|---|---|---|
 | `step_processing` | `worker` | 8 | metadata extraction, dispatch, fast tasks (< 5s) |
-| `thumbnail_rendering` | `render-worker` | 1 | ALL Blender calls — never queue Blender on step_processing |
+| `asset_pipeline` | `render-worker` | 1 | ALL Blender calls — never queue Blender on step_processing |
 
 ### New DB Fields
 - Migration required → list as a separate task with migration filename
@@ -86,7 +86,7 @@ Every new backend response schema needs a TypeScript interface in `frontend/src/
 process_step_file (step_processing)
   → domains/pipeline/tasks/extract_metadata.py
   → queues render_step_thumbnail
-render_step_thumbnail (thumbnail_rendering)
+render_step_thumbnail (asset_pipeline)
   → domains/pipeline/tasks/render_thumbnail.py
   → render-worker: export_step_to_gltf.py (OCC/GMSH tessellation)
   → render-worker: export_gltf.py (Blender: materials, seams, sharp edges)