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/utils/componentHelpers/miniPlayerHelpers.ts

@@ -73,10 +73,3 @@ export function initialSnapshot(): MiniSyncPayload {
     };
   }
 }
-
-export function fmt(seconds: number): string {
-  if (!isFinite(seconds) || seconds < 0) seconds = 0;
-  const m = Math.floor(seconds / 60);
-  const s = Math.floor(seconds % 60);
-  return `${m}:${s.toString().padStart(2, '0')}`;
-}