ui: upgrade to FontAwesome 6, harden burger-menu shim

- Drop FA4 font files and font-awesome.min.css.
- Ship FA6 webfonts (solid, regular, brands) and fa6.min.css.
- io-indicator: use FA6 names (fa-circle-plus / -minus / -exclamation).
- static/js/ui.js: no-op the legacy side-menu click handler when menu
  links are not present (V09 chrome removes them) so the Settings tab
  no longer logs 'cannot set properties of null'.

src/static/css/Audiowide.css

@@ -2,5 +2,5 @@
   font-family: 'Audiowide';
   font-style: normal;
   font-weight: 400;
-  src: local('Audiowide'), local('Audiowide-Regular'), url(http://fonts.gstatic.com/s/audiowide/v4/8XtYtNKEyyZh481XVWfVOqCWcynf_cDxXwCLxiixG1c.ttf) format('truetype');
+  src: local('Audiowide'), local('Audiowide-Regular'), url(https://fonts.gstatic.com/s/audiowide/v4/8XtYtNKEyyZh481XVWfVOqCWcynf_cDxXwCLxiixG1c.ttf) format('truetype');
 }