fix(bridge): 3 bug âm thanh Qin/Nexus standalone

1) wavesynth tự phát khi mở app: probe calibrate() render vào live mix
   (renderAll process cùng instance) -> thêm calibratingCh_[16], renderAll
   bỏ qua channel đang calibrate; plugin_host panic (sustain off + all
   notes off + 128 noteOff) ngay sau preset apply để startup im lặng.
2) bấm GUI mở 2 cửa sổ Qin: sandbox VST2 child tự sở hữu top-level window
   -> ownsGuiWindow() + main.cpp forward OPEN_GUI control, không tạo native
   parent / không registry double-open.
3) play phát nhạc cụ sai: restore clobber — seed preset đè patch thật trong
   state file (ch3 63ba3667 -> 7f07473c) do saveStateJob chạy lúc child còn
   seed. Fix: queuePreset(waitApply=true) chờ child apply xong (presetOut
   memcmp), consume-before-apply (zero presetInLen trước khi apply), deferred
   double-load re-check trong main.cpp skip assign trùng path, watchdog
   respawn re-queue lastPreset_.

native_bridge/include/NativeInstrumentEngine.h

@@ -177,6 +177,7 @@ private:
     // Per-instrument scratch so engines that overwrite (not mix) stay additive.
     std::vector<float> scratchL_, scratchR_;
     // Channel-level reload flag (see isReloading) — indexed by MIDI channel.
+    bool calibratingCh_[16] = {};  // probe-render mute: renderAll skips channel during calibrate()
     bool reloadingCh_[16] = {};
     // G3.3: channel muted after a plugin fault inside processAudioBlock.
     bool crashedCh_[16] = {};
@@ -188,4 +189,4 @@ private:
     std::atomic<bool> isBypassed_{false};
 };
 
-#endif // NATIVE_INSTRUMENT_ENGINE_H
+#endif // NATIVE_INSTRUMENT_ENGINE_H