feat(blog): implement scheduled and draft posts filtering and preview UI

app/[locale]/blog/[slug]/page.tsx

@@ -69,6 +69,11 @@ export default async function BlogPost({ params }: BlogPostProps) {
         category={post.frontmatter.category}
         readingTime={getReadingTime(post.content)}
       />
+      {(new Date(post.frontmatter.date) > new Date() || post.frontmatter.public === false) && (
+        <div className="bg-orange-500 text-white text-center py-2 px-4 font-bold text-sm tracking-wider uppercase relative z-50">
+          Preview (Not visible in production)
+        </div>
+      )}
       {/* Featured Image Header */}
       {post.frontmatter.featuredImage ? (
         <div className="relative w-full h-[70vh] min-h-[500px] overflow-hidden group">