Improve wiki sidebar and TOC (#25460) (#25477)

Backport #25460 by @wxiaoguang

Close #20976
Close #20975

1. Fix the bug: the TOC in footer was incorrectly rendered as main
content's TOC
2. Fix the layout: on mobile, the TOC is put above the main content,
while the sidebar is put below the main content
3. Auto collapse the TOC on mobile

ps: many styles of "wiki.css" are moved from old css files, so leave
nits to following PRs.

### for desktop


![image](6c84201c-0648-465a-99e6-c53cdaee53c0)

### for mobile


![image](9cb4fdfe-b6ab-4e6f-ae82-219ddb8fa27e)

### other changed pages

<details>


![image](ef077736-2c3e-4e3d-82fe-d9bf1ebcca98)


![image](bb528429-ad5f-4258-a5c4-05f997c624ea)

</details>

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

web_src/js/modules/fomantic.js

@@ -3,6 +3,8 @@ import {initAriaCheckboxPatch} from './aria/checkbox.js';
 import {initAriaDropdownPatch} from './aria/dropdown.js';
 import {svg} from '../svg.js';
 
+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;