feat(P2): USD Foundation — canonical part identity + material overrides

M1 — USD exporter:
- render-worker/scripts/export_step_to_usd.py (631 lines)
  Full XCAF traversal, one UsdGeom.Mesh per leaf part,
  schaeffler:partKey on every prim, index-space sharpEdgeVertexPairs
- render-worker/Dockerfile: usd-core>=24.11 installed (USD 0.26.3)

M2 — usd_master MediaAsset + pipeline auto-chain:
- migrations 060 (usd_master enum), 061 (3 JSONB columns),
  062 (rename tessellation settings keys)
- generate_usd_master_task: runs export_step_to_usd.py, upserts
  usd_master MediaAsset, writes resolved_material_assignments to CadFile
- Auto-chained from generate_gltf_geometry_task after every GLB export
- step_tasks.py shim re-exports generate_usd_master_task

M3 — scene-manifest API:
- part_key_service.py: build_scene_manifest(), generate_part_key(),
  four-layer material priority resolution with provenance
- SceneManifest / PartEntry Pydantic models in products/schemas.py
- GET /api/cad/{id}/scene-manifest endpoint (graceful fallback to
  parsed_objects when USD not yet generated)
- POST /api/cad/{id}/generate-usd-master endpoint
- frontend/src/api/sceneManifest.ts: fetchSceneManifest(),
  triggerUsdMasterGeneration()

M4 — manual-material-overrides API:
- GET/PUT /api/cad/{id}/manual-material-overrides endpoints
- CadFile.manual_material_overrides JSONB column (migration 061)
- getManualOverrides() / saveManualOverrides() in cad.ts

M5 — ThreeDViewer partKey integration:
- export_step_to_gltf.py injects partKeyMap into GLB extras
- ThreeDViewer: partKeyMap extraction, resolvePartKey(), effectiveMaterials
  merges legacy partMaterials + new manualOverrides (server-side persistence)
- MaterialPanel: dual-path save (partKey vs legacy), provenance badge,
  reconciliation panel for unmatched/unassigned parts

Also:
- Admin.tsx: generate-missing-usd-masters + canonical scenes bulk actions
- ProductDetail.tsx: usd_master row in asset table
- vite-env.d.ts: fix ImportMeta.env TypeScript error
- GPUProbeResult: add timestamp/devices/render_time_s fields

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

render-worker/scripts/turntable_render.py

@@ -342,6 +342,18 @@ def main():
         except Exception:
             pass
 
+    # Named argument: --usd-path <path> — when set, import USD instead of GLB
+    usd_path = ""
+    if "--usd-path" in argv:
+        _usd_idx = argv.index("--usd-path")
+        usd_path = argv[_usd_idx + 1] if _usd_idx + 1 < len(argv) else ""
+
+    # Pre-load USD import helper once (used in both MODE A and MODE B)
+    _import_usd_file = None
+    if usd_path:
+        sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
+        from import_usd import import_usd_file as _import_usd_file  # type: ignore[assignment]
+
     os.makedirs(frames_dir, exist_ok=True)
 
     try:
@@ -387,8 +399,11 @@ def main():
         # Find or create target collection
         target_col = _ensure_collection(target_collection)
 
-        # Import OCC GLB (already in metres, one object per STEP part)
-        parts = _import_glb(glb_path)
+        # Import geometry: USD path when available, otherwise GLB
+        if usd_path and _import_usd_file:
+            parts = _import_usd_file(usd_path)
+        else:
+            parts = _import_glb(glb_path)
         # Apply render position rotation before material/camera setup
         _apply_rotation(parts, rotation_x, rotation_y, rotation_z)
         # Apply OCC topology-based shading overrides
@@ -466,7 +481,10 @@ def main():
         needs_auto_camera = True
         bpy.ops.wm.read_factory_settings(use_empty=True)
 
-        parts = _import_glb(glb_path)
+        if usd_path and _import_usd_file:
+            parts = _import_usd_file(usd_path)
+        else:
+            parts = _import_glb(glb_path)
         # Apply render position rotation before material/camera setup
         _apply_rotation(parts, rotation_x, rotation_y, rotation_z)
         # Apply OCC topology-based shading overrides