feat(PBR): extract Blender PBR properties and apply in 3D viewer

Extract Base Color, Metallic, Roughness, Transmission, IOR from Blender
asset library materials via catalog_assets.py. Store in catalog JSON and
serve via /api/asset-libraries/pbr-map endpoint. Frontend viewers apply
PBR properties to Three.js MeshStandardMaterial using hex color strings
(avoiding Three.js ColorManagement sRGB/linear issues).

Key fixes:
- RLS bypass for material alias lookup in pbr-map endpoint
- pbrMap empty guard prevents premature grey fallback in viewers
- Cache-Control: no-cache on pbr-map requests to avoid stale data

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

frontend/src/pages/CadPreview.tsx

@@ -27,14 +27,6 @@ export default function CadPreviewPage() {
     refetchInterval: generating ? 3_000 : false,
   })
 
-  // Load production GLB if available
-  const { data: productionAssets } = useQuery({
-    queryKey: ['media-assets', id, 'gltf_production'],
-    queryFn: () => getMediaAssets({ cad_file_id: id!, asset_types: ['gltf_production'] }),
-    enabled: !!id,
-    staleTime: 30_000,
-  })
-
   // Load blend assets for download
   const { data: blendAssets } = useQuery({
     queryKey: ['media-assets', id, 'blend_production'],
@@ -66,7 +58,6 @@ export default function CadPreviewPage() {
   }
 
   const latestGltf = gltfAssets?.[0]
-  const latestProduction = productionAssets?.[0]
   const latestBlend = blendAssets?.[0]
 
   // While checking for assets, show a neutral loading screen (don't attempt to render ThreeDViewer)
@@ -80,7 +71,7 @@ export default function CadPreviewPage() {
   }
 
   // No GLB at all — show generate prompt
-  if (!latestGltf && !latestProduction) {
+  if (!latestGltf) {
     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">
@@ -129,14 +120,11 @@ export default function CadPreviewPage() {
       cadFileId={id}
       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,
       }}
     />