Smoother waveform: 256 samples + interpolated segment-distance line

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/audio.js

@@ -50,7 +50,7 @@ class AudioEngine {
     this.spectrum = new Float32Array(this.NB);
 
     // Time-domain waveform (oscilloscope), -1..1.
-    this.NW = 128;
+    this.NW = 256;
     this.wave = new Float32Array(this.NW);
     this.timeData = new Uint8Array(this.analyser.fftSize);
   }