Refactor "htmx" to "fetch action" (#37208)

The only remaining (hard) part is "templates/repo/editor/edit.tmpl", see the FIXME

By the way:

* Make "user unfollow" use basic color but not red color, indeed it is not dangerous
* Fix "org folllow" layout (use block gap instead of inline gap)

templates/base/head.tmpl

@@ -23,7 +23,7 @@
 	{{template "base/head_script" .}}
 	{{template "custom/header" .}}
 </head>
-<body hx-swap="outerHTML" hx-push-url="false">
+<body>
 	{{template "custom/body_outer_pre" .}}
 
 	<div class="full height">