Winui Setup

It's idempotent, so you can safely rerun it after a Windows reset or when another skill complains about missing prerequisites. The smart bit is that it detects everything up front in parallel, shows you a table of what's installed versus what's missing, then only installs the gaps. It always upgrades WinApp CLI and the templates to latest even if they're present, since the other winui skills assume current versions. One catch: enabling Developer Mode requires UAC elevation, so it asks permission first instead of surprising you with a prompt.