Give the backend modules the container padding of Contao 5.7

The content card no longer pads its children, so the import, inbox and
export modules use the same spacing as the core listing containers.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

public/wk-sync-backend.css

@@ -1,5 +1,6 @@
-.wk-sync { padding: 0 0 1rem; }
+.wk-sync { padding: 18px 15px; }
 .wk-sync h2 { margin: 1.5rem 0 .75rem; font-size: 1.1rem; }
+.wk-sync > h2:first-child, .wk-sync > .tl_message + h2 { margin-top: 0; }
 .wk-sync h3 { margin: 1.25rem 0 .5rem; }
 .wk-sync-nav, .wk-sync-folders { display: flex; flex-wrap: wrap; gap: .5rem; margin: .5rem 0 1rem; }
 .wk-sync-nav .active, .wk-sync-folders .active { background: var(--contao-primary, #f47c00); color: #fff; border-color: transparent; }