feat: native host bridge integration — C++ bridge, Rust SHM, JS routing, build scripts, docs

- native_bridge/: InstrumentEngineManager multi-channel, sample-accurate, CC/program/pitchbend, transport, Vst3Instrument stub (HAVE_VST3SDK)
- src-tauri: shm.rs, bridge spawn + audio pump + health monitor, open_vst_gui, externalBin, commands
- app: UnifiedMidiRouter, NativeBridgeService, bridgeAudioNode, audioRoutingEngine, Plugin Manager UI, Bridge/WASM indicator, set_position sync
- build: 3 ps1 (force-added, build/ ignored), verify_bundle --check-bridge, CI workflow
- docs: TASKS.md, TEST_NOTES.md (Windows verify checklist), install/report updates

native_bridge/include/INativeInstrument.h

@@ -0,0 +1,42 @@
+// native_bridge/include/INativeInstrument.h
+#ifndef I_NATIVE_INSTRUMENT_H
+#define I_NATIVE_INSTRUMENT_H
+
+#include <cstdint>
+#include <string>
+
+enum class InstrumentType {
+    VST3,
+    VST2,
+    SOUNDFONT_SF2_SF3,
+    SFZ
+};
+
+class INativeInstrument {
+public:
+    virtual ~INativeInstrument() = default;
+
+    // Initialize Engine with Sample Rate and Buffer Size
+    virtual bool init(double sampleRate, uint32_t maxBlockSize) = 0;
+
+    // Select Bank and Program Change
+    virtual void selectProgram(uint32_t channel, uint32_t bank, uint32_t program) = 0;
+
+    // Dispatch MIDI Note On / Note Off events
+    virtual void noteOn(uint32_t channel, uint32_t pitch, float velocity, uint32_t sampleOffset) = 0;
+    virtual void noteOff(uint32_t channel, uint32_t pitch, uint32_t sampleOffset) = 0;
+
+    // MIDI continuous controllers (A12): CC value, program change, 14-bit pitch bend
+    virtual void controlChange(uint32_t channel, uint32_t cc, uint32_t value) = 0;
+    virtual void programChange(uint32_t channel, uint32_t program) = 0;
+    virtual void pitchBend(uint32_t channel, uint32_t bend14) = 0;
+
+    // Open/close Native GUI window
+    virtual bool openGUI(void* parentWindowHandle) = 0;
+    virtual void closeGUI() = 0;
+
+    // Real-time Audio PCM Float32 rendering loop
+    virtual void processAudioBlock(float* outputL, float* outputR, uint32_t numSamples) = 0;
+};
+
+#endif // I_NATIVE_INSTRUMENT_H