refactor(bridge): split fx bridge, stabilize VST3 host chain, drop old install engines

- remove diagnostic canaries from audio hot path (crackle fix) and
  stuck C5 note raw-MIDI test (Vst2Instrument::init noteOff)
- split native bridge into daw_vst_bridge (VSTi) + fx_vst_bridge (VST FX)
- VST3: processData prepare before setActive, zero input buses, accept
  both .vstpreset and bridge-state blob in RenderJob presets
- native_render/vst_engine: bridge-exe discovery + render_fx_chain + /fx-gui
- delete old install/ engine binaries (install via sidecar+resources now)
- add BUILD_LAYOUT.md, build_selfcheck, tools/ diagnostics

build/scripts/build_windows.ps1

@@ -57,8 +57,8 @@ if ($LASTEXITCODE -ne 0) { Write-Host "ERROR: bridge sidecar missing" -Foregroun
 npm install -D @tauri-apps/cli
 # Frontend host: copy template -> src-tauri/ui/index.html (giu Tauri context,
 # document.write UI engine; neu thieu -> window mat __TAURI__ -> bridge chet).
-Copy-Item buildscriptsfrontend_host_index.html src-tauriuiindex.html -Force
-if (-not (Test-Path src-tauriuiindex.html)) { Write-Host "ERROR: frontend host missing" -ForegroundColor Red; exit 1 }
+Copy-Item build\scripts\index.html src-tauri\ui\index.html -Force
+if (-not (Test-Path src-tauri\ui\index.html)) { Write-Host "ERROR: frontend host missing" -ForegroundColor Red; exit 1 }
 npx tauri build
 
 Write-Host ""