refactor: replace Fomantic modal with native dialog (#39846)

Replace Fomantic's hard-forked jQuery modal with native `<dialog>`
elements, advancing https://github.com/go-gitea/gitea/issues/29849. The
UI is visually unchanged. Dialogs open with `show()` over an `inert`
page, so tooltips, popups and toasts mounted on `<body>` stay usable
above them, unlike with `showModal()`
(https://github.com/whatwg/html/issues/9936).

- Remove the Fomantic modal and dimmer, add `showModal` and `hideModal`
- Declare modals as `<dialog class="modal-dialog">`, shown inside a
`.modal-backdrop`, instead of `ui modal` with its unused size classes
- Remove two modals that could never be opened
- Block the page while a modal is open, close the topmost one on Escape
and restore focus to its opener
- Allow stacked modals, use a confirm modal instead of `window.confirm`
for deleting content history
- Hide popups and toasts when a modal opens or closes
- Keep the release notes modal open when generating notes fails

Fixes: https://github.com/go-gitea/gitea/issues/39643
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/features/admin/common.ts

@@ -1,7 +1,7 @@
 import {checkAppUrl} from '../common-page.ts';
 import {hideElem, queryElems, showElem, toggleElem} from '../../utils/dom.ts';
 import {POST} from '../../modules/fetch.ts';
-import {showFomanticModal} from '../../modules/fomantic/modal.ts';
+import {showModal} from '../../modules/modal.ts';
 import {pathEscape} from '../../utils/url.ts';
 import {registerGlobalInitFunc} from '../../modules/observer.ts';
 
@@ -274,7 +274,7 @@ function initAdminNotice() {
   const pageContent = document.querySelector('.page-content.admin.notice');
   if (!pageContent) return;
 
-  const detailModal = document.querySelector<HTMLDivElement>('#detail-modal')!;
+  const detailModal = document.querySelector<HTMLDialogElement>('#detail-modal')!;
 
   // Attach view detail modals
   queryElems(pageContent, '.view-detail', (el) => el.addEventListener('click', (e) => {
@@ -282,7 +282,7 @@ function initAdminNotice() {
     const elNoticeDesc = el.closest('tr')!.querySelector('.notice-description')!;
     const elModalDesc = detailModal.querySelector('.content pre')!;
     elModalDesc.textContent = elNoticeDesc.textContent;
-    showFomanticModal(detailModal);
+    showModal(detailModal);
   }));
 
   // Select actions