fix: stopAll cancels scheduled notes, loop works on all tabs

- Add _scheduledNotes array tracking
- stopAll clears all pending setTimeout notes + allNotesOff()
- Loop enabled on MAIN SESSION, SECTION-TAB, PIANO_ROLL via
  isLoopingSelection + selLeft/selRight auto-derivation

app/static/js/services/soundfontPlayer.js

@@ -35,6 +35,7 @@
     let _initialized = false;
     let _initPromise = null;
     let _currentSfId = null;
+    const _scheduledNotes = [];
 
     const SonicSF = {
         loadedFonts: {},
@@ -168,16 +169,28 @@
             const durSec = durationMs / 1000;
             const now = ctx.currentTime;
             const delay = (typeof startTime === 'number' && startTime > now) ? (startTime - now) : 0;
+            const noteId = { on: null, off: null };
+            _scheduledNotes.push(noteId);
             const doNote = () => {
                 try {
                     _synthInstance.noteOn(channel, midiPitch, midiVel);
-                    setTimeout(() => { try { _synthInstance.noteOff(channel, midiPitch); } catch (e) {} }, durSec * 1000);
+                    noteId.off = setTimeout(() => {
+                        try { _synthInstance.noteOff(channel, midiPitch); } catch (e) {}
+                        const idx = _scheduledNotes.indexOf(noteId);
+                        if (idx >= 0) _scheduledNotes.splice(idx, 1);
+                    }, 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();
+            if (delay > 0) {
+                noteId.on = setTimeout(doNote, delay * 1000);
+            } else {
+                doNote();
+                const idx = _scheduledNotes.indexOf(noteId);
+                if (idx >= 0) _scheduledNotes.splice(idx, 1);
+            }
         },
 
         _playNoteOsc: function (note, velocity, durationMs, startTime, program, destinationNode, channel, synthEngine) {
@@ -257,6 +270,12 @@
             if (_initialized && _synthInstance) {
                 try { for (let ch = 0; ch < 16; ch++) _synthInstance.allNotesOff(ch); } catch (e) {}
             }
+            // Cancel all scheduled future notes
+            while (_scheduledNotes.length > 0) {
+                const n = _scheduledNotes.pop();
+                if (n.on) { clearTimeout(n.on); n.on = null; }
+                if (n.off) { clearTimeout(n.off); n.off = null; }
+            }
             const ctx = getCtx();
             const now = ctx.currentTime;
             Object.values(activeOscillators).forEach(entry => {