Scope the entrypoint edit check's buttons; fit the type row at 360px

The browser test's entrypoint edit check clicked any Cancel and Save
on the page, which now also match the add target form's hidden
buttons, so the clicks timed out. It finds them inside the edit form.

The type choice takes p-2 and flex-1 in place of w-32, so it, Next
and Cancel share one row on a 360px-wide phone with "Database" shown
in full.

Model: opus-5-5

templates/source_detail.html

@@ -133,11 +133,13 @@
                  and the hidden type field submitted with them, exist
                  only while that type is chosen. A refused submission
                  comes back open on its type, with the values entered;
-                 Cancel empties the form. -->
+                 Cancel empties the form. The type choice's p-2, narrower
+                 than an input's own padding, keeps it, Next and Cancel on
+                 one row on a 360px-wide phone. -->
             <form method="POST" action="/hook/{{.Webhook.ID}}/targets" x-ref="form">
                 <input type="hidden" name="csrf_token" value="{{.CSRFToken}}">
                 <div x-show="choosing" x-cloak class="p-4 bg-gray-50 border-b border-gray-200 flex flex-wrap gap-2">
-                    <select x-ref="type" aria-label="Target type" class="input text-sm w-32">
+                    <select x-ref="type" aria-label="Target type" class="input text-sm p-2 flex-1">
                         <option value="http">HTTP</option>
                         <option value="slack">Slack</option>
                         <option value="database">Database</option>