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/include/Vst3Instrument.h

@@ -28,6 +28,7 @@ public:
     bool reloadForGUI() override;
     bool attachView(void* parentWindowHandle) override;
     void closeGUI() override;
+    void setChannel(uint32_t ch) { channel_ = ch; }
     bool needsReload() const override { return hasAttachedOnce_ && !guiAttached_; }
     void setReloading(bool on) override { reloading_ = on; }
     void processAudioBlock(float* outputL, float* outputR, uint32_t numSamples) override;
@@ -42,6 +43,7 @@ private:
     bool guiAttached_;
     bool hasAttachedOnce_;
     bool reloading_; // guarded by InstrumentEngineManager::mu_ (set via setReloading)
+    uint32_t channel_ = 0;
     bool reload();
 };