enhance(ui): cleanup navbar template and styling (#39554)

Clean up the navbar template and styling, and fix the navbar stopwatch,
which navigated to the issue instead of opening its popup since
https://github.com/go-gitea/gitea/pull/36965.

1. Add hover background to the create and user menus
2. Simplify navbar HTML and CSS and remove Fomantic styles
3. Render the notification and stopwatch icons once instead of separate
mobile and desktop copies
4. Make the stopwatch a keyboard accessible button whose popup updates
on push and closes when the stopwatch stops

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: bircni <bircni@icloud.com>

web_src/js/vitest.setup.ts

@@ -9,7 +9,6 @@ window.config = {
   customEmojis: {},
   pageData: {},
   notificationSettings: {MinTimeout: 0, TimeoutStep: 0, MaxTimeout: 0},
-  enableTimeTracking: true,
   mermaidMaxSourceCharacters: 5000,
   i18n: {},
   frontendInited: false,