fix(uat-02-01): await async jamClient methods to fix NaN values

Fixes UAT-002: Player showing NaN:NaN and slider positioning incorrectly

Root Cause: jam-ui's jamClientProxy uses Proxy pattern where ALL methods
return Promises (via sendWhenReady → sendMessage → deferred.promise). Code
was calling SessionGetTracksPlayDurationMs(), SessionCurrrentPlayPosMs(),
and isSessionTrackPlaying() synchronously without await.

Result: Promise objects were passed to formatTime() and slider calculations,
causing NaN values and incorrect slider behavior.

Solution:
- Wrapped initialization duration fetch in async function with await
- Changed polling setInterval callback to async function with await for all calls
- Now correctly awaits all jamClient Promise-based methods

This matches jam-ui's async jamClient architecture (different from legacy
web's synchronous bridge API).

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

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

@@ -43,20 +43,24 @@ const JKSessionBackingTrackPlayer = ({
       setCurrentTime('0:00');
       setCurrentPositionMs(0);
 
-      // Fetch and set duration immediately when track loads
-      try {
-        const durationInMs = jamClient.SessionGetTracksPlayDurationMs();
-        console.log('JKSessionBackingTrackPlayer: Duration from jamClient:', durationInMs, 'Type:', typeof durationInMs);
+      // Fetch and set duration immediately when track loads (async)
+      const fetchDuration = async () => {
+        try {
+          const durationInMs = await jamClient.SessionGetTracksPlayDurationMs();
+          console.log('JKSessionBackingTrackPlayer: Duration from jamClient:', durationInMs, 'Type:', typeof durationInMs);
 
-        // Ensure we have a valid number
-        const validDuration = (durationInMs != null && !isNaN(durationInMs) && durationInMs >= 0) ? durationInMs : 0;
-        setDurationMs(validDuration);
-        setDuration(formatTime(validDuration));
-      } catch (error) {
-        console.error('Error fetching track duration:', error);
-        setDuration('0:00');
-        setDurationMs(0);
-      }
+          // Ensure we have a valid number
+          const validDuration = (durationInMs != null && !isNaN(durationInMs) && durationInMs >= 0) ? durationInMs : 0;
+          setDurationMs(validDuration);
+          setDuration(formatTime(validDuration));
+        } catch (error) {
+          console.error('Error fetching track duration:', error);
+          setDuration('0:00');
+          setDurationMs(0);
+        }
+      };
+
+      fetchDuration();
     }
   }, [isOpen, backingTrack, jamClient]);
 
@@ -65,14 +69,15 @@ const JKSessionBackingTrackPlayer = ({
     let intervalId = null;
 
     if (isPlaying && jamClient) {
-      // Start polling when playing
-      intervalId = setInterval(() => {
+      // Start polling when playing (async)
+      intervalId = setInterval(async () => {
         try {
           if (!jamClient) return;
 
-          const positionMs = jamClient.SessionCurrrentPlayPosMs();
-          const durationInMs = jamClient.SessionGetTracksPlayDurationMs();
-          const trackIsPlaying = jamClient.isSessionTrackPlaying();
+          // Await all async jamClient calls
+          const positionMs = await jamClient.SessionCurrrentPlayPosMs();
+          const durationInMs = await jamClient.SessionGetTracksPlayDurationMs();
+          const trackIsPlaying = await jamClient.isSessionTrackPlaying();
 
           console.log('JKSessionBackingTrackPlayer polling:', { positionMs, durationInMs, trackIsPlaying });