feat(01-01): add formatTime utility function for M:SS time display

- Converts milliseconds to M:SS format matching legacy web prettyPrintSeconds
- No padding on minutes (1:02 not 01:02)
- Pads seconds with leading zero when needed

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

jam-ui/src/components/client/JKSessionBackingTrackPlayer.js

@@ -22,6 +22,14 @@ const JKSessionBackingTrackPlayer = ({
 
   const volumeRef = useRef(null);
 
+  // Utility function to format milliseconds to M:SS format
+  const formatTime = (ms) => {
+    const seconds = Math.floor(ms / 1000);
+    const minutes = Math.floor(seconds / 60);
+    const remainingSeconds = seconds % 60;
+    return `${minutes}:${remainingSeconds.toString().padStart(2, '0')}`;
+  };
+
   useEffect(() => {
     if (isOpen && backingTrack) {
       // Initialize player state when opened