fix: piano roll playback now uses musical time instead of absolute seconds

The Part events were pre-converted to seconds via Tone.Time().toSeconds(),
making the BPM setting ineffective. Now uses bars:quarters:sixteenths
notation so the Transport BPM actually controls playback speed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/PianoRollWidget.jsx

@@ -242,20 +242,31 @@ export default function PianoRollWidget({ moduleId }) {
 
     Tone.getTransport().bpm.value = bpm;
 
-    // Build Tone.Part from notes
-    const events = notesRef.current.map(n => ({
-      time: `0:0:${n.start * 4}`, // convert beats to 16th notes for Tone
+    // Build Tone.Part from notes using musical time (bars:quarters:sixteenths)
+    // This lets the Transport BPM control actual playback speed
+    const events = notesRef.current.map(n => {
+      // Convert beats to bars:quarters:sixteenths notation
+      const totalSixteenths = Math.round(n.start * 4);
+      const barNum = Math.floor(totalSixteenths / 16);
+      const remainder = totalSixteenths % 16;
+      const quarterNum = Math.floor(remainder / 4);
+      const sixteenthNum = remainder % 4;
+      return {
+        time: `${barNum}:${quarterNum}:${sixteenthNum}`,
         note: n.note,
         dur: n.duration,
-    }));
+      };
+    });
 
-    // Use a simpler approach: schedule directly
     const part = new Tone.Part((time, ev) => {
       setSequencerSignals(moduleId, midiToFreq(ev.note), true);
+      // Note-off: convert duration beats to musical time for proper BPM-relative timing
+      const durSixteenths = Math.round(ev.dur * 4);
+      const noteOffTime = time + (durSixteenths * (60 / (bpm * 4))) * 0.9;
       Tone.getTransport().scheduleOnce(() => {
         setSequencerSignals(moduleId, midiToFreq(ev.note), false);
-      }, time + Tone.Time(`0:0:${ev.dur * 4}`).toSeconds() * 0.9);
-    }, events.map(ev => [Tone.Time(ev.time).toSeconds(), { note: ev.note, dur: ev.dur }]));
+      }, noteOffTime);
+    }, events.map(ev => [ev.time, { note: ev.note, dur: ev.dur }]));
 
     part.loop = loop;
     part.loopEnd = `${bars}m`;