fix: enable standalone output and remove public directory copy

- Re-enable output: 'standalone' in next.config.ts for Docker builds
- Remove public directory copy from Dockerfile (not needed for this project)
- Standalone mode works with force-dynamic routing to prevent SSR issues

Fixes Gitea Actions build failure where .next/standalone was not found

next.config.ts

@@ -2,8 +2,7 @@ import type { NextConfig } from 'next';
 
 const nextConfig: NextConfig = {
   reactStrictMode: true,
-  // Note: Using default mode (not standalone) to avoid SSR issues with client components
-  // For Docker, we'll use regular server mode which works fine
+  output: 'standalone',
 };
 
 export default nextConfig;