fix(a11y): settings items without href

[userquin]

Any anchor without href cannot be traversed with the keyboard.

This PR uses custom nuxt link and vue component for button when button attr configured: the Show intro "link" cannot be activated using the keyboard (maybe there is a shorcut)

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[shuuji3]

Any anchor without href cannot be traversed with the keyboard.

This is actually the correct behavior in browsers:

Some focusable HTML elements have a default tabindex value of 0 set under the hood by the user agent. These elements are an or with href attribute, (...)

https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/tabindex#:~:text=a%20logical%20sequence.-,Some%20focusable%20HTML%20elements,-have%20a%20default

So maybe setting tabindex="0" or changing <a> to <button> can be a simpler way instead of handling focus event by JavaScript.

I also noticed that some <SettingsItem> are rendered as <a disabled="false" ...>. This false is an invalid value for the disabled property and has the same effect as disabled="true" (ref. Explicitly set disabled="false" in the HTML does not work - Stack Overflow - https://stackoverflow.com/questions/32745276/explicitly-set-disabled-false-in-the-html-does-not-work/32745315#32745315). This may affect the focusable property because the disabled element is skipped to be focused. I'm going to make a PR to fix this attribute.

[userquin]

The html markup is wrong, we're using an anchor when it is a button, check other pages, we dont use anchor for render theme color buttons