Refactor htmx and fetch-action related code (#37186)

This is the first step (the hardest part):

* repo file list last commit message lazy load
* admin server status monitor
* watch/unwatch (normal page, watchers page)
* star/unstar (normal page, watchers page)
* project view, delete column
* workflow dispatch, switch the branch
* commit page: load branches and tags referencing this commit

The legacy "data-redirect" attribute is removed, it only makes the page
reload (sometimes using an incorrect link).

Also did cleanup for some devtest pages.

web_src/js/features/repo-diff-commit.ts

@@ -4,7 +4,7 @@ import {GET} from '../modules/fetch.ts';
 async function loadBranchesAndTags(area: Element, loadingButton: Element) {
   loadingButton.classList.add('disabled');
   try {
-    const res = await GET(loadingButton.getAttribute('data-fetch-url')!);
+    const res = await GET(loadingButton.getAttribute('data-url')!);
     const data = await res.json();
     hideElem(loadingButton);
     addTags(area, data.tags);