fix: schedule SpessaSynth noteOn by startTime via setTimeout

Root cause: timeline play passes exactAudioTime as 4th param which
SpessaSynth interprets as enableReverh (boolean). All notes at T=0.
Fix: compute delay = startTime - ctx.currentTime, use setTimeout
to call noteOn(channel, pitch, vel) at correct future time.
Never pass startTime to noteOn() — SpessaSynth doesn't support it.

app/static/js/services/soundfontPlayer.js

@@ -159,13 +159,18 @@
             }
             if (channel === undefined) channel = 0;
             const durSec = durationMs / 1000;
-            try {
+            const now = ctx.currentTime;
-                _synthInstance.noteOn(channel, midiPitch, midiVel);
+            const delay = (typeof startTime === 'number' && startTime > now) ? (startTime - now) : 0;
-                setTimeout(() => { try { _synthInstance.noteOff(channel, midiPitch); } catch (e) {} }, durSec * 1000);
+            const doNote = () => {
-            } catch (e) {
+                try {
-                console.warn("[SonicSF] SpessaSynth noteOn error, oscillator fallback:", e);
+                    _synthInstance.noteOn(channel, midiPitch, midiVel);
-                this._playNoteOsc(note, velocity, durationMs, startTime, program, null, channel, synthEngine);
+                    setTimeout(() => { try { _synthInstance.noteOff(channel, midiPitch); } catch (e) {} }, durSec * 1000);
-            }
+                } catch (e) {
+                    console.warn("[SonicSF] SpessaSynth noteOn error:", e);
+                    this._playNoteOsc(note, velocity, durationMs, startTime, program, null, channel, synthEngine);
+                }
+            };
+            if (delay > 0) setTimeout(doNote, delay * 1000); else doNote();
         },
 
         _playNoteOsc: function (note, velocity, durationMs, startTime, program, destinationNode, channel, synthEngine) {