Update app icon to use .icon

[kra-mo]

The macOS icon should be updated to use the new .icon format. The asset to use can be found here: https://github.com/nextcloud/talk-ios/tree/main/NextcloudTalk/AppIcon.icon

See also nextcloud/desktop#10073

[ShGKme]

Just checked, @electron/package supports .icon format since v18.4.0 (August 2025).
But we still need to provide both icons for old macOS compatibility.

But everything is handled by the packager.

I'll check the icon.

[kra-mo]

Not sure what tooling that uses, but by default, you do not need to provide 2 different icons, it should generate one:

Xcode automatically generates a similar-looking version of the Liquid Glass icon for previous releases. If you want your existing icon to appear in previous releases, continue to use asset catalogs to represent your app icon.

From https://developer.apple.com/documentation/Xcode/creating-your-app-icon-using-icon-composer