fix(nginx): make Let's Encrypt opt-in per service

certbot cannot issue for internal hostnames (*.nas.local), which made
nginx-enabled services with internal names fail on deploy.

Add a <service>_nginx_letsencrypt flag (default false) and computed
<service>_nginx_ssl_certificate/_key paths: when off the vhost uses the
shared self-signed cert (nginx_default_ssl_cert), when on it uses the
Let's Encrypt lineage. Gate the certbot include on the flag and apply the
pattern to all service roles (deluge, fdroid, gitea, grafana, immich,
metabase, ntfy, prowlarr, radarr, seerr, static_web, uptime_kuma).

roles/static_web/defaults/main.yml

@@ -9,7 +9,10 @@
 #       git_depth: 1  # optional, shallow clone depth
 #       build_command: ""  # optional, command to run after git clone (e.g., npm build)
 #       root_dir: ""  # optional, subdirectory to serve (e.g., "dist" or "build")
-#       ssl_enabled: true  # optional, enable HTTPS with Let's Encrypt (default: true)
+#       ssl_enabled: true  # optional, enable HTTPS (default: true)
+#       letsencrypt: false  # optional, use Let's Encrypt for TLS (default: false,
+#                           # falls back to the shared self-signed cert). Requires
+#                           # a publicly-resolvable hostname.
 
 static_web_sites: {}