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>

frontend/src/pages/Admin.tsx

@@ -73,7 +73,6 @@ export default function AdminPage() {
     blender_eevee_samples: number
     threejs_render_size: number
     thumbnail_format: string
-    stl_quality: string
     blender_smooth_angle: number
     cycles_device: string
     blender_max_concurrent_renders: number
@@ -159,14 +158,6 @@ export default function AdminPage() {
     onError: (e: any) => toast.error(e.response?.data?.detail || 'Import failed'),
   })
 
-  const generateMissingStlsMut = useMutation({
-    mutationFn: () => api.post('/admin/settings/generate-missing-stls'),
-    onSuccess: (res) => {
-      toast.success(res.data.message || 'STL generation queued')
-    },
-    onError: (e: any) => toast.error(e.response?.data?.detail || 'Failed'),
-  })
-
   const reextractMetadataMut = useMutation({
     mutationFn: () => api.post('/admin/settings/reextract-metadata'),
     onSuccess: (res) => {
@@ -397,29 +388,6 @@ export default function AdminPage() {
                 </div>
               </div>
 
-              {/* STL quality */}
-              <div className="flex items-center gap-6 flex-wrap">
-                <span className="text-sm font-medium text-content-secondary w-28 shrink-0">STL quality</span>
-                {(['low', 'high'] as const).map((q) => (
-                  <button
-                    key={q}
-                    onClick={() => setBlenderDraft((d) => ({ ...d, stl_quality: q }))}
-                    className={`px-4 py-1.5 rounded-full border text-sm font-medium transition-colors ${
-                      blender.stl_quality === q
-                        ? 'bg-blue-600 text-white border-blue-600'
-                        : 'bg-surface text-content-secondary border-border-default hover:border-blue-400 hover:text-blue-600'
-                    }`}
-                  >
-                    {q === 'low' ? 'Low (fast)' : 'High (detailed)'}
-                  </button>
-                ))}
-                <p className="text-xs text-content-muted">
-                  {blender.stl_quality === 'high'
-                    ? 'Fine mesh (tol=0.01) — slower STEP→STL, sharper edges.'
-                    : 'Coarse mesh (tol=0.3) — faster, good for previews.'}
-                </p>
-              </div>
-
               {/* Smooth by angle */}
               <div className="flex items-center gap-4 flex-wrap">
                 <span className="text-sm font-medium text-content-secondary w-28 shrink-0">Smooth angle</span>
@@ -704,18 +672,6 @@ export default function AdminPage() {
                 </button>
                 <p className="text-xs text-content-muted">Registers existing renders &amp; CAD thumbnails in the Media Browser.</p>
               </div>
-              <div className="flex flex-col gap-1">
-                <button
-                  onClick={() => generateMissingStlsMut.mutate()}
-                  disabled={generateMissingStlsMut.isPending}
-                  className="btn-secondary text-sm w-full justify-start"
-                  title="Queue STL conversion for every low/high quality that is not yet cached on disk"
-                >
-                  <RefreshCw size={14} className={generateMissingStlsMut.isPending ? 'animate-spin' : ''} />
-                  {generateMissingStlsMut.isPending ? 'Queueing…' : 'Generate Missing STLs'}
-                </button>
-                <p className="text-xs text-content-muted">Generates low + high STL files for completed STEP files missing them.</p>
-              </div>
               <div className="flex flex-col gap-1">
                 <button
                   onClick={() => reextractMetadataMut.mutate()}