fix(bridge): stop leaves sound looping — EventList maxSize=50 drops STOP sweep note-offs

Root cause: Steinberg EventList defaults to maxSize=50 events. The STOP
all-notes-off sweep queues 128 note-offs per channel (16ch x 128 pitch),
so addEvent beyond 50 fails silently and the plugin never receives the
remaining note-offs — voices keep sustaining and the transport loops
forever until the bridge process is killed.

Fix: raise eventList.setMaxSize(4096) in loadPlugin. Also assign unique
noteIds per overlapping note-on (stack per pitch) so note-off releases
every voice at that pitch, and log addEvent result + channel in debug
output for verification.

native_bridge/src/NativeInstrumentEngine.cpp

@@ -168,6 +168,8 @@ bool InstrumentEngineManager::assign(uint32_t channel, InstrumentType type,
         loaded = static_cast<SfizzInstrument*>(inst.get())->loadSfzFile(path, sampleRate);
     else if (type == InstrumentType::VST3)
         loaded = static_cast<Vst3Instrument*>(inst.get())->loadPlugin(path, sampleRate);
+    if (type == InstrumentType::VST3)
+        static_cast<Vst3Instrument*>(inst.get())->setChannel(channel);
     if (!loaded) return false;
     // init() AFTER load: FluidSynth creates its synth inside loadSoundFontFile.
     if (!inst->init(sampleRate, blockSize)) return false;