Polish admin articles: card grid, thumbnails, author, slug field

Replace the plain articles table with a responsive card grid showing
thumbnails, title, date and author. Add a slug field to the article form
with live auto-suggestion, i18n-driven labels, a larger image preview and
delete confirmation. Persist a user-provided slug (falls back to an
auto-generated one) on create and update.

src/app/admin/articles/[id]/page.tsx

@@ -67,6 +67,7 @@ export default async function EditArticle({
 				}}
 				defaultValues={{
 					title: article.title,
+					slug: article.slug,
 					image: article.image,
 					shortStory: article.shortStory,
 					fullStory: article.fullStory,