fix: GUI VST native window qua bridge + audio path bridge (SF2 preview/play câm)

- open_vst_gui: bo WebviewWindowBuilder/thread, chi push_control type=4 (hwnd=0 -> bridge tao window)
- main.cpp: create_native_vst_window (class SonicForge_Native_VST3_Class, 800x600, khong TOPMOST),
  tao trong ChannelWorker job, map guiWindows, capture arg2 by value (fix dangling)
- app.jsx: guard isBridgeActive() 8 cho -> bridge active thi moi note di router -> pushEvent -> bridge
  (truoc day SF2 cam vi HAS_PYFLUIDSYNTH=FALSE -> /soundfont-render 501; VST3 path cu dung nativeSf/Carla)
- E2E: SF2 NOTE_ON qua dispatchMidiEvent -> SHM peak 0.029745; Nexus GUI native hwnd OK (license/preset)
- docs: TASKS.md + TEST_NOTES.md ghi batch fix + ket qua; gitignore vendor/junk

build/scripts/build_windows.ps1

@@ -34,10 +34,14 @@ Copy-Item "dist\daw_engine\*" "src-tauri\resources\daw_engine\" -Recurse -Force
 
 Write-Host "== [5/7] Build native bridge (daw_vst_bridge.exe) =="
 & (Join-Path $PSScriptRoot "build_native_bridge.ps1")
+Set-Location (Join-Path $PSScriptRoot "..\..")   # restore CWD (child script must not leak it)
 if ($LASTEXITCODE -ne 0) { Write-Host "ERROR: native bridge build failed" -ForegroundColor Red; exit 1 }
 if (-not (Test-Path "src-tauri\binaries\daw_vst_bridge-x86_64-pc-windows-msvc.exe")) {
   Write-Host "ERROR: bridge sidecar missing" -ForegroundColor Red; exit 1
 }
+if (-not (Test-Path "src-tauri\binaries\libfluidsynth-3.dll")) {
+  Write-Host "ERROR: libfluidsynth-3.dll missing (bridge runtime DLL)" -ForegroundColor Red; exit 1
+}
 
 Write-Host "== [6/7] VC++ Redistributable for hooks.nsh =="
 if (-not (Test-Path src-tauri\vc_redist.x64.exe)) {
@@ -51,6 +55,10 @@ if (-not (Test-Path "src-tauri\binaries\daw_vst_bridge-x86_64-pc-windows-msvc.ex
 python tools\verify_bundle.py --check-bridge
 if ($LASTEXITCODE -ne 0) { Write-Host "ERROR: bridge sidecar missing" -ForegroundColor Red; exit 1 }
 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 }
 npx tauri build
 
 Write-Host ""