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.

app/core/vst_engine.py

@@ -470,10 +470,13 @@ class PluginManager:
         return presets[:256]
 
     def list_available(self) -> dict:
+        plugins = self._scan_plugins()
         return {
             "vst_instruments": [
-                {"id": k, "name": k, "type": "VST3", "has_native_support": HAS_PEDALBOARD}
-                for k in self._scan_plugins().keys()
+                {"id": k, "name": k,
+                 "type": "VST3" if p.lower().endswith(".vst3") else "VST2",
+                 "has_native_support": HAS_PEDALBOARD}
+                for k, p in plugins.items()
             ],
             "soundfonts": self._scan_soundfonts()
         }