feat: show live progress while downloading named files

Bunny/cross-origin downloads are fetched into a blob before saving, which
on large files or slow connections looked stuck (spinner only). Stream the
body through a counting transform and show real byte progress in a toast:
per-file percent for single downloads and file N/M + percent for bulk.

- Progress is measured from Content-Length + received bytes (not estimated).
- The blob is assembled by the browser from the stream (can be disk-backed),
  so we don't accumulate chunks in the JS heap.
- Only the blob path shows a toast; same-origin (R2/S3/MinIO) and the >10 GB
  fallback use the browser's native download UI.

lib/client/project-download.ts

@@ -4,6 +4,15 @@ import { downloadNamedFile, navigateDownload } from '@/lib/client/download-file'
 
 const DOWNLOAD_STAGGER_MS = 500;
 
+export type ManifestDownloadProgress = {
+  /** 1-based index of the file currently downloading. */
+  index: number;
+  total: number;
+  fileName: string;
+  receivedBytes: number;
+  totalBytes: number | null;
+};
+
 export type ProjectDownloadManifestFile = {
   fileName: string;
   url: string;
@@ -21,10 +30,14 @@ function sleep(ms: number): Promise<void> {
   return new Promise((resolve) => window.setTimeout(resolve, ms));
 }
 
-async function triggerBrowserDownload(file: ProjectDownloadManifestFile): Promise<void> {
+async function triggerBrowserDownload(
+  file: ProjectDownloadManifestFile,
+  onProgress?: (received: number, total: number | null) => void
+): Promise<void> {
   // Same-origin proxy files (R2 / S3 / MinIO via /api/upload/video/...): the
   // download attribute applies and the browser streams straight to disk, so the
-  // name is correct at any size with no memory cost.
+  // name is correct at any size with no memory cost (browser shows its own
+  // progress, so we don't track bytes here).
   if (file.url.startsWith('/api/upload/video/')) {
     navigateDownload(file.url, file.fileName);
     return;
@@ -33,17 +46,39 @@ async function triggerBrowserDownload(file: ProjectDownloadManifestFile): Promis
   // Bunny (CDN redirect) and external direct hosts are cross-origin, so the name
   // only applies if we fetch the bytes. downloadNamedFile does that for files up
   // to 10 GB; larger ones fall back to a plain navigation (CDN filename).
-  const saved = await downloadNamedFile(file.url, file.fileName);
+  const saved = await downloadNamedFile(file.url, file.fileName, (p) =>
+    onProgress?.(p.receivedBytes, p.totalBytes)
+  );
   if (!saved) {
     navigateDownload(file.url, file.fileName);
   }
 }
 
-export async function runProjectDownloadManifest(manifest: ProjectDownloadManifest): Promise<void> {
-  for (let index = 0; index < manifest.files.length; index += 1) {
+export async function runProjectDownloadManifest(
+  manifest: ProjectDownloadManifest,
+  onProgress?: (progress: ManifestDownloadProgress) => void
+): Promise<void> {
+  const total = manifest.files.length;
+  for (let index = 0; index < total; index += 1) {
+    const file = manifest.files[index]!;
+    onProgress?.({
+      index: index + 1,
+      total,
+      fileName: file.fileName,
+      receivedBytes: 0,
+      totalBytes: file.sizeBytes,
+    });
     // Sequential so at most one file is buffered in memory at a time.
-    await triggerBrowserDownload(manifest.files[index]!);
-    if (index < manifest.files.length - 1) {
+    await triggerBrowserDownload(file, (received, fileTotal) =>
+      onProgress?.({
+        index: index + 1,
+        total,
+        fileName: file.fileName,
+        receivedBytes: received,
+        totalBytes: fileTotal,
+      })
+    );
+    if (index < total - 1) {
       await sleep(DOWNLOAD_STAGGER_MS);
     }
   }