Let an entrypoint's description be edited in place (closes #392)

Each entrypoint on the webhook page has an Edit button that shows its
description as a form, with Save and Cancel, in place. Edit hides while
the form is open, and going back to the page does not put unsaved text
back into it, so the form always opens on the saved description.
Saving posts to /hook/{id}/entrypoints/{entrypointID}/edit, behind the
same login, CSRF and ownership checks as activate, deactivate and
delete, and writes only the description column, so the URL never
changes. An empty description shows as "Entrypoint". Activate and
deactivate now write only the active column, so they cannot write back
an older description over an edit.

Model: opus-5-5

static/js/app.js

@@ -70,7 +70,8 @@ document.addEventListener("alpine:init", function () {
     "use strict";
 
     // Something a click shows and hides: the mobile menu, an add form,
-    // an event in the event log, a delivery's attempts.
+    // an entrypoint's edit form, an event in the event log, a delivery's
+    // attempts.
     window.Alpine.data("collapsible", function () {
         return {
             open: false,