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>

render-worker/scripts/export_blend.py

@@ -1,14 +1,14 @@
-"""Blender headless script: export a STEP-derived scene as a production .blend.
+"""Blender headless script: export a geometry GLB as a production .blend.
 
 Usage:
     blender --background --python export_blend.py -- \\
-        --stl_path /path/to/file.stl \\
+        --glb_path /path/to/geometry.glb \\
         --output_path /path/to/output.blend \\
         [--asset_library_blend /path/to/library.blend] \\
         [--material_map '{"SrcMat": "LibMat"}']
 
 The script:
-1. Imports the STL file (with mm→m scale).
+1. Imports the geometry GLB (already in metres, Y-up).
 2. Optionally applies asset library materials from a .blend.
 3. Packs all external data.
 4. Saves a copy as the output .blend.
@@ -28,7 +28,8 @@ def parse_args() -> argparse.Namespace:
         sys.exit(1)
     rest = argv[argv.index("--") + 1:]
     parser = argparse.ArgumentParser()
-    parser.add_argument("--stl_path", required=True)
+    parser.add_argument("--glb_path", required=True,
+                        help="Geometry GLB from export_step_to_gltf.py (already in metres)")
     parser.add_argument("--output_path", required=True)
     parser.add_argument("--asset_library_blend", default=None)
     parser.add_argument("--material_map", default="{}")
@@ -44,14 +45,8 @@ def main() -> None:
     # Clean scene
     bpy.ops.wm.read_factory_settings(use_empty=True)
 
-    # Import STL
-    bpy.ops.import_mesh.stl(filepath=args.stl_path)
-
-    # Scale mm → m
-    for obj in bpy.context.selected_objects:
-        obj.scale = (0.001, 0.001, 0.001)
-        bpy.context.view_layer.objects.active = obj
-        bpy.ops.object.transform_apply(scale=True)
+    # Import geometry GLB (metres, Y-up — no rescaling needed)
+    bpy.ops.import_scene.gltf(filepath=args.glb_path)
 
     # Apply asset library materials if provided
     if args.asset_library_blend and material_map: