fix: resolve blob URLs in designMD before Remotion render

- introVideoUrl, outroVideoUrl, logoUrl, brandAudioUrl can contain
  blob: URLs from the brand editor that Remotion can't access
- Now uploads these to Express and replaces with persistent URLs
- Uses correct Express origin for Electron compatibility

src/hooks/useExportQueue.ts

@@ -124,9 +124,43 @@ export function useExportQueue() {
     // Resolve blob: URLs to persistent server URLs before sending to server-side render
     const resolvedElements = await resolveBlobUrls(config.timelineElements);
 
+    // Also resolve blob URLs in designMD (introVideoUrl, outroVideoUrl, logoUrl)
+    const resolvedDesignMD = { ...config.designMD };
+    const designMDUrlFields: (keyof typeof resolvedDesignMD)[] = [
+      'introVideoUrl', 'outroVideoUrl', 'logoUrl', 'brandAudioUrl',
+    ];
+    for (const field of designMDUrlFields) {
+      const val = resolvedDesignMD[field];
+      if (typeof val === 'string' && val.startsWith('blob:')) {
+        try {
+          const res = await fetch(val);
+          const blob = await res.blob();
+          const ext = blob.type.includes('video') ? '.mp4'
+            : blob.type.includes('audio') ? '.mp3'
+            : blob.type.includes('png') ? '.png'
+            : '.jpg';
+          const file = new File([blob], `designmd-${String(field)}${ext}`, { type: blob.type });
+          const formData = new FormData();
+          formData.append('file', file);
+          const uploadRes = await fetch('/api/upload', { method: 'POST', body: formData });
+          if (uploadRes.ok) {
+            const data = await uploadRes.json();
+            // Use Express origin for Remotion compatibility
+            const electronAPI = (window as any).electronAPI;
+            const origin = electronAPI?.isElectron
+              ? 'http://127.0.0.1:3000'
+              : window.location.origin;
+            (resolvedDesignMD as any)[field] = `${origin}${data.url}`;
+          }
+        } catch (err) {
+          console.warn(`Failed to resolve blob for designMD.${String(field)}:`, err);
+        }
+      }
+    }
+
     // Strip non-serializable props for render (callbacks, refs, etc.)
     const inputProps = {
-      designMD: config.designMD,
+      designMD: resolvedDesignMD,
       textOverlay: config.textOverlay,
       timelineElements: resolvedElements,
       layers: config.layers,