fix: MIDI NoteOff stops note immediately (60000ms duration + stopNote)

- NoteOn: durationMs=60000 (1 phút, giữ cho đến khi NoteOff)
- NoteOff: stopNote(ch, pitch) gọi synthInstance.noteOff() ngay
- MIDI channel (msg.data[0] & 0x0F) truyền đúng vào playNote
- CC (sustain/modulation) + pitch bend forward qua SpessaSynth

app/static/js/services/soundfontPlayer.js

@@ -161,6 +161,13 @@
             }
         },
 
+        stopNote: function (channel, pitch) {
+            if (channel < 0 || channel > 15) return;
+            if (_initialized && _synthInstance) {
+                try { _synthInstance.noteOff(channel, pitch); } catch (e) {}
+            }
+        },
+
         playNote: function (note, velocity, durationMs, startTime, program, destinationNode, channel, synthEngine) {
             if (_initialized && _synthInstance) {
                 this._playNoteSpessa(note, velocity, durationMs, startTime, program, channel, synthEngine);