enh: Suppress logging for ACME challenge requests in nginx configs

[nfebe]

Context

From PR #109 review.

ACME challenge requests generate noise in nginx access/error logs, especially 404s for challenges that have been cleaned up. These should be suppressed.

Locations

• internal/nginx/manager.go — all 6 ACME challenge location blocks in templates
• templates/infra/nginx/default.conf — default server ACME challenge location

Expected

Add logging suppression to all ACME challenge locations:

location /.well-known/acme-challenge/ {
    root /usr/share/nginx/html;
    access_log off;
    log_not_found off;
}