feat(ebook): improve search UX with grid actions and Enter-to-submit

Add a two-column grid layout for the admin protected-phrases actions
and submit the search form on Enter (Shift+Enter for newline).

python/ebook_search/api/templates/admin.html

@@ -52,7 +52,7 @@ head %}
 </section>
 <section>
   <h2>Protected phrases</h2>
-  <section class="actions">
+  <section class="actions actions-grid">
     <form
       hx-post="/admin/phrases/generate-all"
       hx-target="#admin-status"