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

An entrypoint's description was set when it was added and could never change, so renaming one meant deleting it and adding a new one with a new URL every sender had to be given again. Each entrypoint on the webhook page now has an Edit button, in the shared secondary style, that opens its description in place with Save and Cancel and keeps its URL. The save goes through the same login, CSRF and ownership checks as the other entrypoint actions; an empty description shows as "Entrypoint". Activate and deactivate now write only the active column, so they cannot undo an edit. Tests cover each, through the router and the browser.

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,