fix(glb): remove invalid export_colors param + fix viewer stale mesh

4 root causes fixed:

1. export_colors=False was removed in Blender 4.x — caused every Blender
   export to fail (exit 1) and always fall back to trimesh. Remove it.
   Blender now runs the full pipeline: materials + sharp edges.

2. GlbModel cloned ref never reset on url change — key={glbBlobUrl} forces
   React to remount GlbModel on each new blob URL, resetting the ref so
   fresh geometry is always loaded.

3. glbBlobUrl not cleared before re-fetch — setGlbBlobUrl(null) added at
   start of downloadUrl effect so spinner shows instead of stale mesh.

4. staleTime: 30_000 delayed picking up new MediaAsset after generation.
   Changed to staleTime: 0 so invalidation always triggers immediate refetch.

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

frontend/src/components/cad/InlineCadViewer.tsx

@@ -96,7 +96,7 @@ export default function InlineCadViewer({
   const { data: gltfAssets } = useQuery({
     queryKey: ['media-assets', cadFileId, 'gltf_geometry'],
     queryFn: () => getMediaAssets({ cad_file_id: cadFileId, asset_types: ['gltf_geometry'] }),
-    staleTime: 30_000,
+    staleTime: 0,
     refetchInterval: generating ? 4_000 : false,
   })
 
@@ -109,6 +109,8 @@ export default function InlineCadViewer({
 
   useEffect(() => {
     if (!downloadUrl || !token) return
+    // Clear stale mesh immediately so the loading spinner shows instead of old geometry
+    setGlbBlobUrl(null)
     setLoadingGlb(true)
     let blobUrl = ''
     fetch(downloadUrl, { headers: { Authorization: `Bearer ${token}` } })
@@ -140,7 +142,7 @@ export default function InlineCadViewer({
         <Canvas camera={{ position: [0, 0, 2], fov: 45 }}>
           <Suspense fallback={null}>
             <Environment preset={lightPreset} background={false} />
-            <GlbModel url={glbBlobUrl} wireframe={viewMode === 'wireframe'} />
+            <GlbModel key={glbBlobUrl} url={glbBlobUrl} wireframe={viewMode === 'wireframe'} />
           </Suspense>
           <OrbitControls makeDefault />
         </Canvas>