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.

routers/web/repo/watch.go

@@ -26,6 +26,5 @@ func ActionWatch(ctx *context.Context) {
 		ctx.ServerError("GetRepositoryByName", err)
 		return
 	}
-	ctx.RespHeader().Add("hx-trigger", "refreshUserCards") // see the `hx-trigger="refreshUserCards ..."` comments in tmpl
 	ctx.HTML(http.StatusOK, tplWatchUnwatch)
 }