fix: convert master meter levels to dB scale for consistent metering

Previously, master meters received raw linear values (0-1) while track
meters received dB-normalized values, causing inconsistent metering display.
Now both master peak and RMS levels are converted using linearToDbScale()
for accurate comparison between track and master levels.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

lib/hooks/useMultiTrackPlayer.ts

@@ -152,14 +152,15 @@ export function useMultiTrackPlayer(
     // Detect clipping (signal >= 1.0)
     const isClipping = peak >= 1.0;
 
-    setMasterPeakLevel(peak);
-    setMasterRmsLevel(rms);
+    // Convert to dB scale (same as track levels) for consistent metering
+    setMasterPeakLevel(linearToDbScale(peak));
+    setMasterRmsLevel(linearToDbScale(rms));
     if (isClipping) {
       setMasterIsClipping(true);
     }
 
     masterLevelMonitorFrameRef.current = requestAnimationFrame(monitorMasterLevels);
-  }, []);
+  }, [linearToDbScale]);
 
   // Apply automation values during playback
   const applyAutomation = useCallback(() => {