Moves the WixUI_Minimal UI and finish-screen launch checkbox out of
main.wxs into a dedicated ui.wxs fragment, referenced from main.wxs via
<UIRef Id='OpenCADStudioUI'>. Keeps the package/feature definition and
the UI concerns in separate files.
Updates the release workflow to compile both .wxs files (candle now
writes per-source .wixobj into a directory) and link both objects.
https://claude.ai/code/session_01DFVSKgViFaxEjZD2KsTdtt
