Fix mobile navbar and misc cleanups (#25134) (#25169)

Backport #25134 by @silverwind

- Fix and improve mobile navbar layout
- Apply all cleanups suggested in
https://github.com/go-gitea/gitea/pull/25111
- Make media query breakpoints match Fomantic's exactly
- Clean up whitespace in class on navbar items

Mobile navbar before and after:
<img width="745" alt="Screenshot 2023-06-08 at 08 40 56"
src="ca84b239-b10f-41db-8c06-dcf2b6dd9d28">
<img width="739" alt="Screenshot 2023-06-08 at 08 41 23"
src="09133c54-eb7e-4110-858c-ead23c3b7521">

web_src/js/features/repo-issue.js

@@ -476,7 +476,6 @@ export function initRepoPullRequestReview() {
       content: $panel[0],
       placement: 'bottom',
       trigger: 'click',
-      role: 'menu',
       maxWidth: 'none',
       interactive: true,
       hideOnClick: true,