fix: disable SpessaSynth playback, use oscillator for client preview

- SpessaSynth bank loading fails in AudioWorklet for unknown reason
- Set _initialized=false after init so playNote uses oscillator path
- Server-side FluidSynth render produces authentic SoundFont audio on Export

app/static/js/services/soundfontPlayer.js

@@ -44,11 +44,8 @@
             if (_initInProgress) return;
             _initInProgress = true;
             if (!window.SpessaSynthClass || !window.__SpessaSynthCDN) {
-                console.warn("[SonicSF] SpessaSynth CDN not loaded. Retrying in 2s...");
+                console.warn("[SonicSF] SpessaSynth CDN not loaded. Using oscillator fallback.");
                 _initInProgress = false;
-                setTimeout(() => {
-                    if (!_initialized && window.SpessaSynthClass && audioContext) this.init(audioContext);
-                }, 2000);
                 return;
             }
             try {
@@ -56,27 +53,50 @@
                 await audioContext.audioWorklet.addModule(procUrl);
                 _synthInstance = new window.SpessaSynthClass(audioContext);
                 await _synthInstance.isReady;
+                // Try loading default SGM bank to verify SpessaSynth works
+                try {
+                    const resp = await fetch("/api/v1/plugins/soundfonts/download/sgm_v2.01?t=" + Date.now());
+                    if (resp.ok) {
+                        const buf = await resp.arrayBuffer();
+                        await _synthInstance.soundBankManager.addSoundBank(buf.slice(0), "sgm_v2.01");
+                        await _synthInstance.isReady;
+                        const bankCount = _synthInstance.soundBankManager?.soundBankList?.length ?? 0;
+                        if (bankCount > 0) {
                             _initialized = true;
                             _initInProgress = false;
-                console.log("[SonicSF] SpessaSynth initialized.");
+                            console.log("[SonicSF] SpessaSynth ready with", bankCount, "banks.");
+                            return;
+                        }
+                    }
+                } catch (bankErr) {
+                    console.warn("[SonicSF] Default bank load failed:", bankErr);
+                }
+                console.log("[SonicSF] SpessaSynth init OK but bank load failed. Using oscillator.");
             } catch (e) {
-                _initInProgress = false;
                 console.warn("[SonicSF] AudioWorklet init failed:", e);
                 try {
                     const mod = await import("https://cdn.jsdelivr.net/npm/spessasynth_lib@4.3.1/dist/index.js");
                     _synthInstance = new mod.WorkerSynthesizer(audioContext);
                     await _synthInstance.isReady;
-                    _initialized = true;
+                    console.log("[SonicSF] WorkerSynthesizer ready (oscillator fallback for playback).");
-                    console.log("[SonicSF] SpessaSynth initialized via Worker.");
                 } catch (e2) {
                     console.error("[SonicSF] All SpessaSynth paths failed:", e2);
                 }
             }
+            // Always reset initialized — playNote falls through to oscillator
+            _initialized = false;
+            _initInProgress = false;
         },
 
         selectInstrument: async function (channel, bank, program, sfId) {
             if (!_initialized || !_synthInstance) return;
-            if (sfId) await this.loadSoundFont(sfId);
+            if (sfId) {
+                const ok = await this.loadSoundFont(sfId);
+                if (!ok) {
+                    console.warn("[SonicSF] selectInstrument: bank not loaded, oscillator will be used.");
+                    return;
+                }
+            }
             try { _synthInstance.controllerChange(channel, 0, bank); } catch (e) {}
             try { _synthInstance.controllerChange(channel, 32, 0); } catch (e) {}
             try { _synthInstance.programChange(channel, program); } catch (e) {}