feat: GPU rendering + material matching + perf improvements

- GPU: fix Cycles device activation order — set compute_device_type
  BEFORE engine init, re-set AFTER open_mainfile wipes preferences
- GPU: remove _mark_sharp_and_seams edit-mode loop (redundant with
  Blender 5.0 shade_smooth_by_angle), saves ~200s/render on 175 parts
- Material: fix _AFN suffix mismatch — build AF-stripped mat_map keys
  and add prefix fallback in _apply_material_library (blender_render.py)
- Material: production GLB now uses get_material_library_path() which
  checks active AssetLibrary instead of empty legacy system setting
- Admin: RenderTemplateTable multi-select output types (M2M frontend)
- Admin: MaterialLibraryPanel replaced with link to Asset Libraries
- UX: move Toaster to top-left to avoid dispatch button overlap
- SQLAlchemy: add .unique() to all RenderTemplate M2M collection queries
- Logging: flush=True on all Blender progress prints, stdout reconfigure

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

frontend/src/pages/CadPreview.tsx

@@ -79,8 +79,8 @@ export default function CadPreviewPage() {
     )
   }
 
-  // No GLB available yet — show generate prompt
-  if (!latestGltf) {
+  // No GLB at all — show generate prompt
+  if (!latestGltf && !latestProduction) {
     return (
       <div className="fixed inset-0 z-50 flex flex-col bg-gray-950">
         <div className="flex items-center justify-between px-5 py-3 bg-gray-900 border-b border-gray-800">
@@ -130,8 +130,13 @@ export default function CadPreviewPage() {
       onClose={() => navigate(-1)}
       geometryGltfUrl={latestGltf?.download_url ?? undefined}
       productionGltfUrl={latestProduction?.download_url ?? undefined}
+      hasGeometryGlb={!!latestGltf}
+      hasProductionGlb={!!latestProduction}
+      isGeneratingGeometry={generating}
+      onGenerateGeometry={() => generateMutation.mutate()}
       downloadUrls={{
         glb: latestGltf?.download_url ?? undefined,
+        production: latestProduction?.download_url ?? undefined,
         blend: latestBlend?.download_url ?? undefined,
       }}
     />