feat: remove fomantic's tab module (#8587)

In similar vein of forgejo/forgejo#7416

- Fomantic's tab module is responsible for showing the right content when a tab is clicked upon. Most notably the Write/Preview tabs on the comment editor.
- Remove it and replace the javascript with our own function that is able to provide everything Forgejo needs.
- Replace the CSS with our own bare minimum CSS.
- No functionality or visual is affected by this replacement.
- E2E test added.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8587
Reviewed-by: Otto <otto@codeberg.org>
Reviewed-by: 0ko <0ko@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

web_src/js/modules/fomantic.js

@@ -11,9 +11,6 @@ import {initDimmer} from './dimmer.ts';
 export const fomanticMobileScreen = window.matchMedia('only screen and (max-width: 767.98px)');
 
 export function initGiteaFomantic() {
-  // Silence fomantic's error logging when tabs are used without a target content element
-  $.fn.tab.settings.silent = true;
-
   // By default, use "exact match" for full text search
   $.fn.dropdown.settings.fullTextSearch = 'exact';
   // Do not use "cursor: pointer" for dropdown labels