Implement automated scheduled publishing for blog

- Enhanced blog library to read from both posts/ and scheduled/ directories
- Added publishDate filtering with real-time checking (no cron jobs needed)
- Support for draft posts and recursive directory scanning
- Posts automatically appear when publishDate is reached
- Containerized solution that works without external scheduling
- Added publishDate field to blog types and updated existing scheduled post

Tested and verified:
✅ Past-dated posts appear automatically
✅ Future-dated posts remain hidden until publish time
✅ Draft posts are excluded regardless of date
✅ Maintains existing functionality for regular posts

🤖 Generated with [Claude Code](https://claude.ai/code)

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

app/posts/[slug]/page.tsx

@@ -64,8 +64,8 @@ export default async function PostPage({ params }: PostPageProps) {
       rehypePlugins: [
         rehypeHighlight,
         rehypeSlug,
-        [rehypeAutolinkHeadings, { behavior: 'wrap' }]
-      ],
+        [rehypeAutolinkHeadings, { behavior: 'wrap' } as any]
+      ] as any,
     }
   }