fix: SF2 sound (audio sink FIFO underrun) + VST3 native GUI open + GUI load race

- bridgeAudioNode: ScriptProcessor 4096 drained only 1 of 16 blocks -> ~94% silence; now drains all queued blocks per callback, RING_DEPTH 8->24
- app.jsx: openNativeGUI had NO caller; wire after VST3 loadInstrument OK in track Synth dropdown + Plugin Manager Load Bridge
- main.cpp: OPEN_GUI polls up to 10s for LOAD completion (worker thread) before attach - fixes race 'no instrument loaded'
- index.html: bump bridgeAudioNode/app.precompiled cache versions

app/static/js/app.jsx

@@ -5725,6 +5725,11 @@ const PluginManagerModal = ({ isOpen, onClose, pluginsData, onInsertInstrument }
       const ok = await window.NativeBridgeService.loadInstrument(r.path, type, 0);
       window.showToast && window.showToast(ok ? ('Đã load vào Native Bridge: ' + r.path) : 'Bridge không khả dụng (dev mode?)', ok ? 'success' : 'warning');
       if (ok) window.SonicAPI.bridgeStatus().then(s => setBridgeStatus(s)).catch(() => {});
+      // Requirement 2: VST3 load → mở native GUI ngay (C++ attach editor vào
+      // cửa sổ bridge tự tạo — control type=4, hwnd=0).
+      if (ok && type === 'VST3' && window.NativeBridgeService.openNativeGUI) {
+        try { await window.NativeBridgeService.openNativeGUI(name); } catch (e) {}
+      }
       return ok;
     } catch (err) {
       window.showToast && window.showToast('Lỗi load bridge: ' + (err.message || err), 'error');
@@ -15370,6 +15375,11 @@ const App = () => {
       if (p) {
         const ok = await window.NativeBridgeService.loadInstrument(p, btype, bch);
         console.log('[Bridge] track', trackId, '-> bridge', btype, 'ch', bch, ok ? 'OK' : 'FAIL', p);
+        // Requirement 2: chọn VST3 qua nút Synth → load xong mở native GUI
+        // (C++ attach editor vào cửa sổ bridge tự tạo — control type=4, hwnd=0).
+        if (ok && btype === 'VST3' && window.NativeBridgeService.openNativeGUI) {
+          try { await window.NativeBridgeService.openNativeGUI(instrumentId); } catch (e) {}
+        }
       }
     })();
   };