fix: 3 bugs in Electron export pipeline

Bug 1: RENDERS_DIR mismatch (root cause)
- server.ts had hardcoded renders dir, now reads BRADLY_RENDERS_DIR env
- renderQueue.ts saves to ~/Library/.../Bradly/renders/
- server.ts now serves from the same directory

Bug 2: Upload origin pointing to wrong port
- uploadBlobContent.ts used window.location.origin (Vite 5173)
- Remotion bundler needs Express origin (3000) to access media
- Added getExpressOrigin() helper that detects Electron

Bug 3: Batch ZIP export using file-saver (doesn't work in Electron)
- Added saveBlobFile IPC method (preload + main)
- batchExporter.ts now uses native save dialog in Electron
- Web mode falls back to file-saver

src/utils/batchExporter.ts

@@ -198,7 +198,19 @@ export async function exportBatchAsZip(
     .replace(/\s+/g, '_')
     .replace(/[^a-zA-Z0-9._-]/g, '');
 
-  saveAs(zipBlob, zipName);
+  // In Electron, use native save dialog
+  const electronAPI = (typeof window !== 'undefined') ? (window as any).electronAPI : null;
+  if (electronAPI?.saveBlobFile) {
+    const arrayBuffer = await zipBlob.arrayBuffer();
+    await electronAPI.saveBlobFile(
+      new Uint8Array(arrayBuffer),
+      zipName,
+      [{ name: 'ZIP Archive', extensions: ['zip'] }],
+    );
+  } else {
+    // Web fallback
+    saveAs(zipBlob, zipName);
+  }
 
   onProgress?.({ current: total, total, status: 'done' });
 }

src/utils/uploadBlobContent.ts

@@ -27,6 +27,23 @@ async function blobUrlToFile(blobUrl: string, fallbackName: string): Promise<Fil
   return new File([blob], `${fallbackName}${ext}`, { type: blob.type });
 }
 
+/**
+ * Get the Express server origin for building absolute media URLs.
+ * In Electron dev mode, the renderer runs on Vite (5173) but media
+ * is served by Express (3000). Remotion's bundler needs Express URLs.
+ */
+function getExpressOrigin(): string {
+  if (typeof window !== 'undefined' && (window as any).electronAPI?.isElectron) {
+    // In Electron, Express is always on 127.0.0.1:3000
+    return 'http://127.0.0.1:3000';
+  }
+  // In web mode, Express IS the origin
+  if (typeof window !== 'undefined') {
+    return window.location.origin;
+  }
+  return 'http://localhost:3000';
+}
+
 /**
  * Upload a single File to the server and return an absolute persistent URL.
  * Must be absolute because Remotion's server-side bundler runs on a different
@@ -44,8 +61,7 @@ async function uploadFile(file: File): Promise<string> {
   }
   const data = await res.json();
   // Return absolute URL so Remotion's bundler (different port) can reach it
-  const origin = typeof window !== 'undefined' ? window.location.origin : 'http://localhost:3000';
-  return `${origin}${data.url}`;
+  return `${getExpressOrigin()}${data.url}`;
 }
 
 /**