chore: remove debug endpoints and update configuration

- Removed debug-packages and test-sync API endpoints no longer needed
- Extracted sync status management into shared lib/sync/status module
- Updated Next.js config to remove deprecated experimental appDir flag
- Added port specification to production start script for consistency

next.config.js

@@ -1,8 +1,6 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
-  experimental: {
-    appDir: true,
-  },
+  // App directory is now stable in Next.js 14, no longer experimental
 }
 
 module.exports = nextConfig;