Add VST2 hosting to native bridge; fix CC7 data2 routing verified via SHM test

VST2 (Steinberg 2.4 ABI) host via Vst2Instrument: aeffect.h, dispatcher,
process events/replacing, kEffectStartProcess, headless GUI skip.
- create_instrument returns Vst2Instrument for InstrumentType::VST2
- 64B-aligned scratch buffers for SIMD plugins; SEH crash capture module+stack
- plugins.py: VST2 resolves .dll/.so; vst_engine.py reports VST2 type
- app.jsx: derive instrumentType from scan (VST3 vs VST2), not hardcoded
- Install exes refreshed from Release build

SF2 FluidSynth audio verified end-to-end through SHM ring (energy 1.33):
silence was a test-harness bug (CC7 value written to velocity field, bridge
reads data2) — app sends data2 correctly. All temporary diagnostics removed.

native_bridge/src/Vst2Instrument.h

@@ -0,0 +1,57 @@
+// native_bridge/src/Vst2Instrument.h
+// VST2 (VST 2.4, 64-bit) instrument host. Clean-room ABI header
+// (native_bridge/vestige/aeffect.h) — no Steinberg SDK, no LMMS code.
+// Headless: no GUI editor (openGUI returns false); preset state is kept via
+// effGetChunk/effSetChunk (fxp-style chunks).
+#ifndef VST2_INSTRUMENT_H
+#define VST2_INSTRUMENT_H
+
+#include "INativeInstrument.h"
+
+#include <string>
+#include <vector>
+
+class Vst2Instrument : public INativeInstrument {
+public:
+    Vst2Instrument();
+    ~Vst2Instrument() override;
+
+    bool loadPlugin(const std::string& path, double sampleRate);
+    void setChannel(uint32_t channel) { channel_ = channel; }
+
+    bool init(double sampleRate, uint32_t maxBlockSize) override;
+    void selectProgram(uint32_t channel, uint32_t bank, uint32_t program) override;
+    void noteOn(uint32_t channel, uint32_t pitch, float velocity, uint32_t sampleOffset) override;
+    void noteOff(uint32_t channel, uint32_t pitch, uint32_t sampleOffset) override;
+    void controlChange(uint32_t channel, uint32_t cc, uint32_t value) override;
+    void programChange(uint32_t channel, uint32_t program) override;
+    void pitchBend(uint32_t channel, uint32_t bend14) override;
+    bool openGUI(void* parentWindowHandle) override;
+    bool canOpenGUI() const override { return false; }
+    void closeGUI() override;
+    bool hasAttachedView() const override;
+    void captureState() override;
+    void restoreState() override;
+    std::string serializeState() const override;
+    void loadSerializedState(const std::string& base64) override;
+    void processAudioBlock(float* outputL, float* outputR, uint32_t numSamples) override;
+
+    // Accessors used by the audioMaster callback (same translation unit's
+    // friend-ish helpers) without exposing AEffect* in the header.
+    double sampleRate() const { return sampleRate_; }
+    uint32_t maxBlockSize() const { return maxBlockSize_; }
+    const void* effect() const;  // AEffect*; null until loaded
+
+private:
+    void* state_;          // Vst2HostState* (pimpl — aeffect.h stays out of the header)
+    std::string path_;
+    double sampleRate_;
+    uint32_t maxBlockSize_;
+    bool loaded_;
+    uint32_t channel_ = 0;
+    // scratch buffers for silent plugin inputs
+    std::vector<float> inL_;
+    std::vector<float> inR_;
+};
+
+#endif // VST2_INSTRUMENT_H