refactor: replace STL intermediary with OCC-native STEP→GLB pipeline

- export_step_to_gltf.py: STEP→GLB via RWGltf_CafWriter + BRepBuilderAPI_Transform
  (mm→m pre-scaling, XCAFDoc_ShapeTool.GetComponents_s static method)
- Blender scripts (blender_render.py, still_render.py, turntable_render.py,
  export_gltf.py, export_blend.py): import GLB instead of STL, remove _scale_mm_to_m
- step_tasks.py: add generate_gltf_production_task, remove generate_stl_cache,
  replace _bbox_from_stl with _bbox_from_glb (trimesh), auto-queue geometry GLB
  after thumbnail render
- render_blender.py: replace _stl_from_cache_or_convert with _glb_from_step,
  remove convert_step_to_stl and export_per_part_stls
- domains/rendering/tasks.py: update render_turntable_task, export_gltf/blend tasks
  to use GLB instead of STL
- cad.py: remove STL download/generate endpoints, add generate-gltf-production
- admin.py: generate-missing-stls → generate-missing-geometry-glbs
- Frontend: replace STL cache UI with GLB generate buttons, remove stl_cached field

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

backend/app/api/routers/admin.py

@@ -438,30 +438,36 @@ async def reextract_all_metadata(
     return {"queued": queued, "message": f"Queued {queued} CAD file(s) for metadata re-extraction"}
 
 
-@router.post("/settings/generate-missing-stls", status_code=status.HTTP_202_ACCEPTED)
-async def generate_missing_stls(
+@router.post("/settings/generate-missing-geometry-glbs", status_code=status.HTTP_202_ACCEPTED)
+async def generate_missing_geometry_glbs(
     admin: User = Depends(require_admin),
     db: AsyncSession = Depends(get_db),
 ):
-    """Queue STL generation for every quality missing from each completed CAD file."""
-    from pathlib import Path as _Path
+    """Queue geometry GLB generation for every completed CAD file that has no gltf_geometry MediaAsset."""
+    import uuid as _uuid
+    from app.domains.media.models import MediaAsset, MediaAssetType
+
     result = await db.execute(
         select(CadFile).where(CadFile.processing_status == ProcessingStatus.completed)
     )
     cad_files = result.scalars().all()
 
-    from app.tasks.step_tasks import generate_stl_cache
+    # Bulk-fetch existing gltf_geometry assets
+    existing_result = await db.execute(
+        select(MediaAsset.cad_file_id).where(MediaAsset.asset_type == MediaAssetType.gltf_geometry)
+    )
+    existing_ids = {row[0] for row in existing_result.all()}
+
+    from app.tasks.step_tasks import generate_gltf_geometry_task
     queued = 0
     for cad_file in cad_files:
         if not cad_file.stored_path:
             continue
-        step = _Path(cad_file.stored_path)
-        for quality in ("low", "high"):
-            if not (step.parent / f"{step.stem}_{quality}.stl").exists():
-                generate_stl_cache.delay(str(cad_file.id), quality)
-                queued += 1
+        if cad_file.id not in existing_ids:
+            generate_gltf_geometry_task.delay(str(cad_file.id))
+            queued += 1
 
-    return {"queued": queued, "message": f"Queued {queued} missing STL generation task(s)"}
+    return {"queued": queued, "message": f"Queued {queued} missing geometry GLB task(s)"}
 
 
 @router.post("/settings/seed-workflows", status_code=status.HTTP_200_OK)