Minor perf improvements

[endemic]

• defer CSS loading using the preload relationship
• defer syntax highlighting js loading
• use font-display: swap to see text sooner

[endemic]

Basic asset caching for nginx:

server {
    listen 80;
    server_name yourdomain.com;

    root /var/www/your-site;

    location / {
        try_files $uri $uri/ =404;
    }

    # Cache static assets for 1 year
    location ~* \.(?:css|js|jpg|jpeg|gif|png|ico|woff2?|ttf|svg|eot|otf|webp)$ {
        expires 1y;
        access_log off;
        add_header Cache-Control "public, immutable";
    }
}