feat(preview): implement preview mode for content management

- Added support for a preview mode in the CMS, allowing draft content to be viewed without being indexed.
- Updated hooks and server logic to handle preview parameters, adjusting cache control and robots tags accordingly.
- Enhanced layout to display a preview notification when in preview mode, improving user experience for content editors.

src/hooks.server.ts

@@ -49,9 +49,12 @@ export const handle: Handle = async ({ event, resolve }) => {
     },
   });
 
+  const isPreview = event.url.searchParams.has('preview');
+
   if (
     event.request.method === 'GET' &&
     isCacheablePath(event.url.pathname) &&
+    !isPreview &&
     !response.headers.has('cache-control')
   ) {
     response.headers.set('cache-control', PAGE_CACHE_CONTROL);
@@ -64,7 +67,9 @@ export const handle: Handle = async ({ event, resolve }) => {
   ) {
     response.headers.set(
       'x-robots-tag',
-      'index, follow, max-image-preview:large, max-snippet:-1',
+      isPreview
+        ? 'noindex, nofollow'
+        : 'index, follow, max-image-preview:large, max-snippet:-1',
     );
   }