Replace UWP with WinUI

[BillWagner]

The Windows docs team wants to emphasize WinUI over UWP

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[Copilot]

Pull Request Overview

This PR updates a navigation link in the desktop applications card, replacing the deprecated Universal Windows Platform (UWP) reference with the modern WinUI framework.

Key changes:

• Updated URL from /uwp to /windows/apps/winui
• Changed link text from "Universal Windows apps" to "WinUI apps"

[BillWagner]

/cc @GrantMeStrength

[gewarren]

Probably should update here too:

https://github.com/dotnet/docs-desktop/blob/1419af783e0b1c05e4ce0b80c4d44bc7712bc034/dotnet-desktop-guide/index.yml#L32

https://github.com/MicrosoftDocs/DocsRoot/blob/90d2381daa845ad5fce4adf2260c4e26a9c30df4/content-nav/MSDocsHeader-AspNet.yml#L50

https://github.com/MicrosoftDocs/DocsRoot/blob/90d2381daa845ad5fce4adf2260c4e26a9c30df4/content-nav/MSDocsHeader-DotNetCSharp.yml#L104

https://github.com/MicrosoftDocs/DocsRoot/blob/90d2381daa845ad5fce4adf2260c4e26a9c30df4/content-nav/MSDocsHeader-DotNetMaui.yml#L77

https://github.com/MicrosoftDocs/DocsRoot/blob/90d2381daa845ad5fce4adf2260c4e26a9c30df4/content-nav/MSDocsHeader-DotNet.yml#L86

[BillWagner]

@gewarren I do have a PR open for DocsRoot. I pinged Andy to update the docs-desktop repo.

[adegeo]

dotnet/docs-desktop#2142

I just replaced UWP straight up. The link to the UWP docs is really reference material, it doesn't look like it's promoting learning the technology in any way.