Tweak repo buttons on mobile and labeled button border-radius (#30503)

Fixes: https://github.com/go-gitea/gitea/issues/30514
Fixes:
https://github.com/go-gitea/gitea/pull/30288#issuecomment-2057466623

- Fix border-radius regression from
https://github.com/go-gitea/gitea/pull/30475
- Fix and simplify hover state
- Move the modal HTML so it does not interfere with the CSS
- Make the star and unwatch text show on mobile. There is still plenty
of space, below is iPhone 12 viewport size

<img width="696" alt="Screenshot 2024-04-15 at 20 34 03"
src="https://github.com/go-gitea/gitea/assets/115237/af90bb00-4671-4973-a255-8eb44ee6ba8d">
<img width="230" alt="Screenshot 2024-04-15 at 20 31 42"
src="https://github.com/go-gitea/gitea/assets/115237/986ef533-7a01-4bb0-8dcd-fd19e4259e84">
<img width="233" alt="Screenshot 2024-04-15 at 20 31 47"
src="https://github.com/go-gitea/gitea/assets/115237/5b825dd8-0ccc-4d56-9d8f-774abb935b68">

---------

Co-authored-by: Giteabot <teabot@gitea.io>

templates/repo/star_unstar.tmpl

@@ -4,7 +4,7 @@
 		{{if $.IsStaringRepo}}{{$buttonText = ctx.Locale.Tr "repo.unstar"}}{{end}}
 		<button type="submit" class="ui compact small basic button"{{if not $.IsSigned}} disabled{{end}} aria-label="{{$buttonText}}">
 			{{if $.IsStaringRepo}}{{svg "octicon-star-fill"}}{{else}}{{svg "octicon-star"}}{{end}}
-			<span class="not-mobile" aria-hidden="true">{{$buttonText}}</span>
+			<span aria-hidden="true">{{$buttonText}}</span>
 		</button>
 		<a hx-boost="false" class="ui basic label" href="{{$.RepoLink}}/stars">
 			{{CountFmt .Repository.NumStars}}