fix(nginx): prevent cert leak on IPv6 / unknown SNI

Two issues caused TLS to break on photos.carabosse.cloud over IPv6
(GrapheneOS + Immich app via Orange 5G NAT64):

1. Per-service vhosts only listened on IPv4 (listen 443 ssl). On IPv6,
   nginx fell back to the first vhost loaded alphabetically and served
   its certificate, breaking hostname verification on every other vhost.

2. /etc/letsencrypt/{live,archive} were 0700 root:root after certbot
   created them, so the nginx worker (user http on Arch) could not read
   the chained intermediates and served the leaf-only chain.

Changes:
- Add catch-all 00-default.conf default_server on :80 and :443 (v4+v6)
  with a self-signed cert and 'return 444'. ACME challenges still
  answered on :80.
- Add IPv6 listeners ([::]:80 and [::]:443 ssl) to immich, gitea, ntfy,
  uptime_kuma vhosts and to the temporary ACME provisioning vhost.
- Apply 0755 on /etc/letsencrypt/live and /etc/letsencrypt/archive on
  every run, not only at initial cert provisioning.

roles/nginx/defaults/main.yml

@@ -17,6 +17,12 @@ nginx_client_max_body_size: 100M
 # SSL configuration (volontarily omit TLSv1.2 here)
 nginx_ssl_protocols: TLSv1.3
 
+# Catch-all default_server (rejects unknown SNI / Host with 444).
+# Prevents leaking the first-loaded vhost's cert to unrelated requests.
+nginx_default_server_enabled: true
+nginx_default_ssl_cert: /etc/nginx/ssl/default.crt
+nginx_default_ssl_key: /etc/nginx/ssl/default.key
+
 # Logging configuration
 # Backend: 'file' (traditional /var/log/nginx/*.log) or 'journald' (systemd journal)
 nginx_log_backend: journald