feat: layout hamburger, media browser filters+previews, billing fixes

- Layout: mobile hamburger menu + overlay backdrop + close button; content area always full-width
- Media browser: filter chips (default still+turntable); advanced toggle for GLB/STL; thumbnail_url previews for non-image types; video hover-play for turntable
- Backend: asset_types multi-filter, thumbnail_url in MediaAssetOut, download proxy endpoint for MinIO/local files
- Admin: "Import Existing Media" button → POST /api/admin/import-media-assets
- Billing: fix invoice create 500 (MissingGreenlet — use selectinload after commit); PDF download uses axios blob instead of bare <a href> (auth header missing); fix storage.upload() accepting str|Path
- SSE task logs: task_logs.py core + router, LiveRenderLog component
- CadPreview: fix infinite loop when no gltf_geometry assets; loading screen before ThreeDViewer render
- render-worker: add trimesh layer to Dockerfile

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

frontend/src/components/cad/ThreeDViewer.tsx

@@ -218,8 +218,6 @@ export default function ThreeDViewer({
   productionGltfUrl,
   downloadUrls,
 }: ThreeDViewerProps) {
-  const defaultUrl = `/api/cad/${cadFileId}/model`
-
   const [mode, setMode] = useState<ViewMode>('geometry')
   const [wireframe, setWireframe] = useState(false)
   const [envPreset, setEnvPreset] = useState<EnvPreset>('city')
@@ -231,7 +229,7 @@ export default function ThreeDViewer({
   const activeUrl =
     mode === 'production' && productionGltfUrl
       ? productionGltfUrl
-      : geometryGltfUrl || defaultUrl
+      : geometryGltfUrl
 
   const handleModelReady = useCallback(() => setModelReady(true), [])
   const handleError = useCallback((msg: string) => setLoadError(msg), [])
@@ -372,16 +370,18 @@ export default function ThreeDViewer({
           <directionalLight position={[5, 10, 7]} intensity={1.0} castShadow />
           <directionalLight position={[-5, -5, -5]} intensity={0.25} />
 
-          <GltfErrorBoundary onError={handleError}>
-            <Suspense fallback={null}>
-              <ModelWithReady
-                key={activeUrl}
-                url={activeUrl}
-                wireframe={wireframe}
-                onReady={handleModelReady}
-              />
-            </Suspense>
-          </GltfErrorBoundary>
+          {activeUrl && (
+            <GltfErrorBoundary onError={handleError}>
+              <Suspense fallback={null}>
+                <ModelWithReady
+                  key={activeUrl}
+                  url={activeUrl}
+                  wireframe={wireframe}
+                  onReady={handleModelReady}
+                />
+              </Suspense>
+            </GltfErrorBoundary>
+          )}
 
           <OrbitControls enablePan enableZoom enableRotate minDistance={0.3} maxDistance={100} />
           <Environment preset={envPreset} />