Fix mobile navbar and misc cleanups (#25134)

- 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="https://github.com/go-gitea/gitea/assets/115237/ca84b239-b10f-41db-8c06-dcf2b6dd9d28">
<img width="739" alt="Screenshot 2023-06-08 at 08 41 23"
src="https://github.com/go-gitea/gitea/assets/115237/09133c54-eb7e-4110-858c-ead23c3b7521">

---------

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

web_src/js/components/DashboardRepoList.vue

@@ -12,7 +12,6 @@
         </div>
         <a class="gt-df gt-ac muted" :href="subUrl + '/repo/create' + (isOrganization ? '?org=' + organizationId : '')" :data-tooltip-content="textNewRepo">
           <svg-icon name="octicon-plus"/>
-          <span class="sr-only">{{ textNewRepo }}</span>
         </a>
       </h4>
       <div class="ui attached segment repos-search">
@@ -121,7 +120,6 @@
         </div>
         <a class="gt-df gt-ac muted" v-if="canCreateOrganization" :href="subUrl + '/org/create'" :data-tooltip-content="textNewOrg">
           <svg-icon name="octicon-plus"/>
-          <span class="sr-only">{{ textNewOrg }}</span>
         </a>
       </h4>
       <div v-if="organizations.length" class="ui attached table segment gt-rounded-bottom">