refactor(format): consolidate duration formatters into format/formatDuration (Phase L, part 2) (#690)

The mm:ss track-time formatter was hand-rolled in 11 places and the
h:mm:ss total-duration formatter in 4 — extract two tested functions:

- formatTrackTime(seconds, fallback='0:00')  — m:ss, used for track /
  playback times. fallback param covers the '–' placeholder rows.
- formatLongDuration(seconds)                — h:mm:ss when >=1h, else
  m:ss, used for album / queue totals.

Behaviour preserved per call site: the unified guard
(!seconds || !isFinite || <0 -> fallback) produces identical output to
every prior variant for all real inputs; SongRow keeps its '–' via the
fallback arg. Removes the formatter exports from 6 componentHelpers
files (playerBarHelpers / fullscreenPlayerHelpers deleted — they only
exported the formatter) and 7 inline component copies.

+ formatDuration.test.ts

src/components/MobilePlayerView.tsx

@@ -12,6 +12,7 @@ import {
 } from 'lucide-react';
 import { usePlayerStore } from '../store/playerStore';
 import { useCachedUrl } from './CachedImage';
+import { formatTrackTime } from '../utils/format/formatDuration';
 import LyricsPane from './LyricsPane';
 import { usePlaybackDelayPress } from '../hooks/usePlaybackDelayPress';
 import PlaybackDelayModal from './PlaybackDelayModal';
@@ -66,13 +67,6 @@ function useAlbumAccentColor(imageUrl: string): string {
   return color;
 }
 
-function formatTime(seconds: number): string {
-  if (!seconds || isNaN(seconds)) return '0:00';
-  const m = Math.floor(seconds / 60);
-  const s = Math.floor(seconds % 60);
-  return `${m}:${s.toString().padStart(2, '0')}`;
-}
-
 // ── Queue Drawer ──────────────────────────────────────────────────────────────
 
 function QueueDrawer({ onClose }: { onClose: () => void }) {
@@ -119,7 +113,7 @@ function QueueDrawer({ onClose }: { onClose: () => void }) {
                     </div>
                     <div className="mq-item-artist truncate">{track.artist}</div>
                   </div>
-                  <span className="mq-item-dur">{formatTime(track.duration)}</span>
+                  <span className="mq-item-dur">{formatTrackTime(track.duration)}</span>
                 </div>
               );
             })
@@ -373,8 +367,8 @@ export default function MobilePlayerView() {
           <div className="mp-scrubber-thumb" style={{ left: `${effectiveProgress * 100}%` }} />
         </div>
         <div className="mp-scrubber-times">
-          <span>{formatTime(effectiveTime)}</span>
-          <span>-{formatTime(Math.max(0, duration - effectiveTime))}</span>
+          <span>{formatTrackTime(effectiveTime)}</span>
+          <span>-{formatTrackTime(Math.max(0, duration - effectiveTime))}</span>
         </div>
       </div>