Update layout, navigation, and content for documentation pages

Enhanced the documentation pages by updating the layout with aesthetic adjustments and adding better navigation elements. New documentation content was added: 'Authentication', 'Getting Started', and their child pages. This ensures users have a clearer path when viewing, navigating, and accessing the information they need. "Read more" fallback label was added to the documentation cards for better accessibility.

packages/cms/keystatic/src/client.ts

@@ -72,7 +72,13 @@ export class KeystaticClient implements CmsClient {
       return Promise.resolve(undefined);
     }
 
-    return this.mapPost({ entry: doc, slug: params.slug }, []);
+    const allPosts = await reader.collections[collection].all();
+
+    const children = allPosts.filter(
+      (item) => item.entry.parent === params.slug,
+    );
+
+    return this.mapPost({ entry: doc, slug: params.slug }, children);
   }
 
   async getCategories() {