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/include/INativeInstrument.h

@@ -33,6 +33,9 @@ public:
 
     // Open/close Native GUI window
     virtual bool openGUI(void* parentWindowHandle) = 0;
+    // Headless engines (VST2 without an editor, SF2/SFZ): the bridge must
+    // not create/reuse a window for them.
+    virtual bool canOpenGUI() const { return true; }
     virtual void closeGUI() = 0;
     // VST3 reopen-after-close: the bridge checks before openGUI whether the
     // instance must be rebuilt; while it is, the engine sets reloading=true