bridge: fix Qin VST2 silent playback via per-child SHM sandbox

- out-of-process VST2 sandbox: each Qin track spawns its own plugin_host.exe child
  with unique SHM (SonicForge_PluginHost2_<bridgePid>_<ch>_<seq>), watchdog <=3 respawns
- preset round-trip bridge<->child over SHM (presetIn/presetOut 64KB), stub rejection MIN_PRESET=100
- seed qin_default.b64 default preset into every fresh child; saved patch wins on restore
- forward MIDI on channel 0 (Qin_RV only listens on ch0); one instrument per child
- controls 4/5/6 = OPEN_GUI/CLOSE_GUI/QUIT
- gitignore runtime carla_projects

build/scripts/build_native_bridge.ps1

@@ -79,7 +79,7 @@ cmake -S $NB_DIR -B $BUILD_DIR -G $VS_GEN -A $VS_ARCH `
   -DCMAKE_BUILD_TYPE=Release `
   -DVCPKG_TARGET_TRIPLET=x64-windows
 if ($LASTEXITCODE -ne 0) { Write-Host "ERROR: cmake configure failed" -ForegroundColor Red; exit 1 }
-cmake --build $BUILD_DIR --config Release --target daw_vst_bridge fx_vst_bridge -- /m
+cmake --build $BUILD_DIR --config Release --target daw_vst_bridge fx_vst_bridge plugin_host -- /m
 if ($LASTEXITCODE -ne 0) { Write-Host "ERROR: cmake build failed" -ForegroundColor Red; exit 1 }
 
 # 6. Copy sidecar to Tauri externalBin location
@@ -93,6 +93,10 @@ Copy-Item $EXE (Join-Path $BIN_DIR "daw_vst_bridge-x86_64-pc-windows-msvc.exe")
 $FX_EXE = Join-Path $BUILD_DIR "Release\fx_vst_bridge.exe"
 if (-not (Test-Path $FX_EXE)) { Write-Host "ERROR: $FX_EXE not found" -ForegroundColor Red; exit 1 }
 Copy-Item $FX_EXE (Join-Path $BIN_DIR "fx_vst_bridge-x86_64-pc-windows-msvc.exe") -Force
+# plugin_host: VST sandbox child (VST3 crash isolation + jBridge VST2 per-process instances)
+$PH_EXE = Join-Path $BUILD_DIR "Release\plugin_host.exe"
+if (-not (Test-Path $PH_EXE)) { Write-Host "ERROR: $PH_EXE not found" -ForegroundColor Red; exit 1 }
+Copy-Item $PH_EXE (Join-Path $BIN_DIR "plugin_host-x86_64-pc-windows-msvc.exe") -Force
 
 # 7. Copy runtime DLLs next to sidecar (Tauri externalBin bundles only the exe)
 Write-Host "== [7/7] Copy runtime DLLs (fluidsynth + jpeg) =="