refactor(dedup): consolidate byte / sanitize / clock / album-duration helpers (Phase L, part 2) (#692)

Findings 5-8 of the dedup audit:

- F5 byte formatters: appUpdaterHelpers.fmtBytes + ZipDownloadOverlay
  .formatMB route through the existing formatBytes; a new formatMb
  (always-MB) backs playlistDetailHelpers.formatSize, AlbumHeader and
  the 4 inline DeviceSyncPreSyncModal expressions. SongInfoModal.format
  Size is intentionally left — it uses decimal (1e6) divisors, not 1024.
- F6 sanitizeHtml: extracted to utils/sanitizeHtml.ts; AlbumHeader,
  ComposerDetail and the (now-empty, deleted) artistDetailHelpers use it
  directly. nowPlayingHelpers keeps its own export but now delegates to
  the shared sanitiser and only adds its trailing-link strip on top.
- F7 album duration: BecauseYouLikeRail's formatAlbumDuration drops in
  favour of the shared formatHumanHoursMinutes. Behaviour note: total
  minutes now floor instead of round (<=1 min display difference,
  matches every other caller).
- F8 clock time: extracted to utils/format/formatClockTime.ts;
  PlaybackDelayModal + QueueHeader use it (toLocaleTimeString and
  Intl.DateTimeFormat produced identical output).

Behaviour preserved except the two explicitly noted divergences (F7
round->floor; F5 appUpdater/Zip now show GB above 1 GB instead of a
large MB number).

src/components/ZipDownloadOverlay.tsx

@@ -2,11 +2,7 @@ import { useEffect } from 'react';
 import { createPortal } from 'react-dom';
 import { HardDriveDownload, Check, X } from 'lucide-react';
 import { useZipDownloadStore } from '../store/zipDownloadStore';
-
-function formatMB(bytes: number): string {
-  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(0)} KB`;
-  return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
-}
+import { formatBytes } from '../utils/format/formatBytes';
 
 function ZipDownloadItem({ id }: { id: string }) {
   const dismiss = useZipDownloadStore(s => s.dismiss);
@@ -47,9 +43,9 @@ function ZipDownloadItem({ id }: { id: string }) {
       {!item.done && !item.error && (
         <>
           <div className="zip-dl-info">
-            {formatMB(item.bytes)}
+            {formatBytes(item.bytes)}
             {item.total !== null && item.total > 0 && (
-              <> / {formatMB(item.total)} &nbsp;({pct!.toFixed(0)}%)</>
+              <> / {formatBytes(item.total)} &nbsp;({pct!.toFixed(0)}%)</>
             )}
           </div>
           <div className={`zip-dl-track${isIndeterminate ? ' zip-dl-indeterminate' : ''}`}>