fix: modal accessibility

[Nerixyz]

I noticed that in the SelectEmoteSet modal, the "buttons" don't have any tooltip. This can make discovering the purpose of a button hard. In addition, all the buttons in this dialog are divs. Furthermore, the modal isn't maked as a dialog/modal to the browser.

This PR attempts to fix these issues while maintaining the style of the old buttons. With the core component being UnstyledButton that, as the name suggests, is a button that's styled like a div.

There's one more issue that's out of scope (i think): The dialog should have a focus trap, so elements behind it can't be tabbed. There's a hook in vueuse for it, but at this point why not use something like @headlessui/vue which implements a plain, accessible dialog. Elements behind the dialog cannot be tabbed now.

The PR only modifies the SelectEmoteSet dialog, future PRs could modify other dialog.

[CLAassistant]

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