Fix multi-domain certificate path handling and update nginx to 1.30

[kings9527]

Problem

When multiple domains are configured in the domains array, the script uses unquoted $domains in path operations (e.g., rm -Rf /etc/letsencrypt/live/$domains), which causes bash to expand the array into multiple arguments. This leads to:

1. Incorrect certificate directory resolution — the path becomes /etc/letsencrypt/live/example.org www.example.org instead of /etc/letsencrypt/live/example.org
2. Accidental file deletion — commands like rm -Rf /etc/letsencrypt/archive/$domains attempt to delete paths that don't exist or may match unintended targets
3. False-positive existing data detection — checking $data_path (always exists after first run) instead of the actual certificate directory

Changes

init-letsencrypt.sh

• Use ${domains[0]} as the certificate directory name (Certbot uses the first domain for the live directory)
• Check $data_path/conf/live/$cert_dir for existing certificate detection
• Quote all path references to prevent word splitting on multi-domain arrays
• Display all configured domains in user prompts for clarity

docker-compose.yml

• Update nginx from 1.15-alpine (2018, EOL, vulnerable) to 1.30-alpine (2026 stable, includes HTTP/2 keep-alive improvements)

Related

• Fixes Multiple domains don't really work well! #139 (Multiple domains don't really work well!)
• Addresses the root cause behind several challenge failure reports where certbot could not locate the correct certificate paths

Testing

• Script syntax validated with bash -n
• Multi-domain array expansion verified with test arrays
• Nginx 1.30-alpine image resolves successfully