fix: only send All Notes Off (CC123) when sustain pedal is not active

- Track sustain state per channel via _sustainStates[]
- sustainActive(channel) returns boolean
- MIDI NoteOn: only send CC123 if !sustainActive(ch)
- Preserves sustained notes when playing new notes

app/static/js/services/soundfontPlayer.js

@@ -36,6 +36,7 @@
     let _initPromise = null;
     let _currentSfId = null;
     const _scheduledNotes = [];
+    const _sustainStates = new Array(16).fill(false);
 
     const SonicSF = {
         loadedFonts: {},
@@ -122,6 +123,9 @@
                 _channels[channel].bank = value;
                 _channels[channel].isPercussion = (value === 128);
             }
+            if (controller === 64) {
+                _sustainStates[channel] = value >= 64;
+            }
         },
 
         programChange: function (channel, program) {
@@ -154,6 +158,11 @@
             return { ..._channels[channel] };
         },
 
+        sustainActive: function (channel) {
+            if (channel < 0 || channel > 15) return false;
+            return _sustainStates[channel];
+        },
+
         pitchBend: function (channel, value) {
             if (channel < 0 || channel > 15) return;
             if (_initialized && _synthInstance) {