fix: waveform rendering to respect track duration vs project duration

- Calculate trackWidth based on track duration ratio to project duration
- Shorter tracks now render proportionally instead of stretching
- Longer tracks automatically update project duration
- All existing tracks re-render correctly when duration changes

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

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

components/tracks/Track.tsx

@@ -339,14 +339,18 @@ export function Track({
     } else {
       totalWidth = width;
     }
-    const samplesPerPixel = buffer.length / totalWidth;
+
+    // Calculate how much of the canvas width this track's duration occupies
+    const trackDurationRatio = buffer.duration / duration;
+    const trackWidth = width * trackDurationRatio;
+    const samplesPerPixel = buffer.length / trackWidth;
 
     // Draw waveform
     ctx.fillStyle = track.color;
     ctx.strokeStyle = track.color;
     ctx.lineWidth = 1;
 
-    for (let x = 0; x < width; x++) {
+    for (let x = 0; x < trackWidth; x++) {
       const startSample = Math.floor(x * samplesPerPixel);
       const endSample = Math.floor((x + 1) * samplesPerPixel);