Update card buttons dynamically

User flows when editing a card look like:
- Click "Edit" → the closure buttons are replaced by "Save changes"
- Submit card form → Saves and restores closure buttons
- Press ESC while editing → Cancels and restores closure buttons

Also, renamed for clarity:
- _title.html.erb → _content.html.erb

Co-Authored-By: Claude <noreply@anthropic.com>

app/views/cards/container/_content_display.html.erb

@@ -0,0 +1,9 @@
+<h1 class="card__title flex align-start gap-half">
+  <%= link_to card.title, edit_card_path(card), class: "card__title-link" %>
+</h1>
+
+<% unless card.description.blank? %>
+  <div class="card__description rich-text-content" data-controller="syntax-highlight retarget-links">
+    <%= card.description %>
+  </div>
+<% end %>