Add Qt 6 and NSIS installer batch files for the Windows 11 VM

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

seediso/windows11/Install-NSIS.bat

@@ -0,0 +1,32 @@
+@echo off
+setlocal
+title Install NSIS
+
+fltmc >nul 2>&1
+if errorlevel 1 (
+    echo Please right-click this file and choose "Run as administrator".
+    pause
+    exit /b 1
+)
+
+where winget.exe >nul 2>&1
+if errorlevel 1 (
+    echo winget was not found.
+    pause
+    exit /b 1
+)
+
+echo Installing NSIS with winget...
+winget install --id NSIS.NSIS --exact --source winget ^
+    --accept-source-agreements --accept-package-agreements
+set "RC=%ERRORLEVEL%"
+
+if "%RC%"=="0" (
+    echo Done. Open a new terminal to pick up the updated PATH.
+) else if "%RC%"=="3010" (
+    echo Done. A reboot is required to finish the installation.
+) else (
+    echo winget exited with code %RC%.
+)
+pause
+exit /b %RC%