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-Qt6.bat

@@ -0,0 +1,33 @@
+@echo off
+setlocal
+title Install Qt 6
+
+rem Qt is not available from winget, so this uses the standalone aqtinstall (aqt) to fetch it.
+rem The msvc2022_64 build needs the MSVC Build Tools (see Install-MSVC2022-BuildTools.bat).
+
+set "QT_VERSION=6.8.3"
+set "QT_ARCH=win64_msvc2022_64"
+set "QT_ROOT=C:\Qt"
+set "AQT=%TEMP%\aqt.exe"
+
+echo Downloading aqtinstall...
+curl.exe -L --fail -o "%AQT%" https://github.com/miurahr/aqtinstall/releases/download/v3.3.0/aqt_x64.exe
+if errorlevel 1 (
+    echo Download failed.
+    pause
+    exit /b 1
+)
+
+echo Installing Qt %QT_VERSION% (%QT_ARCH%) to %QT_ROOT% ...
+"%AQT%" install-qt windows desktop %QT_VERSION% %QT_ARCH% --outputdir "%QT_ROOT%"
+set "RC=%ERRORLEVEL%"
+
+del "%AQT%" >nul 2>&1
+
+if "%RC%"=="0" (
+    echo Done. Use -DCMAKE_PREFIX_PATH=%QT_ROOT%\%QT_VERSION%\msvc2022_64 with CMake.
+) else (
+    echo aqt exited with code %RC%.
+)
+pause
+exit /b %RC%