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

templates/source_detail.html

@@ -54,15 +54,29 @@
 
             <div class="divide-y divide-gray-100">
                 {{range .Entrypoints}}
-                <div class="p-4">
+                <div class="p-4" x-data="collapsible">
                     <div class="flex flex-wrap items-center justify-between gap-2 mb-1">
-                        <span class="text-sm font-medium text-gray-900">{{if .Description}}{{.Description}}{{else}}Entrypoint{{end}}</span>
+                        <span x-show="closed" class="text-sm font-medium text-gray-900">{{if .Description}}{{.Description}}{{else}}Entrypoint{{end}}</span>
+                        <!-- Edit shows this form in place of the
+                             description and hides until it closes, and
+                             Cancel resets what was typed. With
+                             autocomplete="off", going back to the page
+                             does not put unsaved text back either, so
+                             the form always opens on the saved
+                             description. -->
+                        <form x-show="open" x-cloak method="POST" action="/hook/{{$.Webhook.ID}}/entrypoints/{{.ID}}/edit" class="flex w-full gap-2">
+                            <input type="hidden" name="csrf_token" value="{{$.CSRFToken}}">
+                            <input type="text" name="description" value="{{.Description}}" autocomplete="off" placeholder="Description (optional)" class="input text-sm flex-1">
+                            <button type="submit" class="btn-primary text-sm">Save</button>
+                            <button type="reset" @click="toggle" class="btn-secondary text-sm">Cancel</button>
+                        </form>
                         <div class="flex flex-wrap items-center gap-2">
                             {{if .Active}}
                             <span class="badge-success">Active</span>
                             {{else}}
                             <span class="badge-error">Inactive</span>
                             {{end}}
+                            <button type="button" x-show="closed" @click="toggle" class="btn-small" title="Edit">Edit</button>
                             <form method="POST" action="/hook/{{$.Webhook.ID}}/entrypoints/{{.ID}}/toggle" class="inline">
                                 <input type="hidden" name="csrf_token" value="{{$.CSRFToken}}">
                                 <button type="submit" class="btn-small" title="{{if .Active}}Deactivate{{else}}Activate{{end}}">