fix: unload old SoundFont before loading new one

- Add _currentSfId tracking
- loadSoundFont calls deleteSoundBank(oldId) before addSoundBank(newId)
- Skip reload if same sfId requested
- Prevents bank accumulation in SpessaSynth

app/static/js/services/soundfontPlayer.js

@@ -34,6 +34,7 @@
     let _synthInstance = null;
     let _initialized = false;
     let _initPromise = null;
+    let _currentSfId = null;
 
     const SonicSF = {
         loadedFonts: {},
@@ -60,7 +61,12 @@
 
         loadSoundFont: async function (sfId) {
             if (!_initialized || !_synthInstance) return false;
+            if (_currentSfId === sfId) return true;
             try {
+                // Unload previous SoundFont
+                if (_currentSfId) {
+                    try { _synthInstance.soundBankManager.deleteSoundBank(_currentSfId); } catch (e) {}
+                }
                 const cache = window.SonicSFStorage;
                 let buf = cache ? await cache.getBuffer(sfId) : null;
                 if (!buf) {
@@ -72,6 +78,7 @@
                 }
                 await _synthInstance.soundBankManager.addSoundBank(buf.slice(0), sfId);
                 await _synthInstance.isReady;
+                _currentSfId = sfId;
                 return true;
             } catch (e) {
                 console.warn("[SonicSF] loadSoundFont failed:", e);