feat: Node.js 24 and 26 images; refuse builds below the Oct 2026 security floor

- One install-node.sh <major> replaces install-node{18,20,22}.sh. It fails the
  build if NodeSource hands back a version below the newest security release
  for the line (22.23.4 / 24.22.1 / 26.12.1: CVE-2026-111497 Brotli OOB write
  and 9 others), so a lagging mirror can't ship a vulnerable image silently.
  18 and 20 are EOL: they still build, with a warning.
- CI matrix adds 24 and 26; fail-fast off so one line can't cancel the rest.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Dockerfile

@@ -18,7 +18,7 @@ RUN chmod +x /scripts/*
 # Generate self-signed cert, create needed dirs, install Node.js, clean up
 RUN openssl req -newkey rsa:2048 -nodes -keyout /etc/pki/tls/private/localhost.key -x509 -days 3650 -subj "/CN=localhost" -out /etc/pki/tls/certs/localhost.crt && \
     mkdir -p /var/log/nodejs && \
-    /scripts/install-node$NODEVER.sh && \
+    /scripts/install-node.sh "$NODEVER" && \
     rm -rf /tmp/*
 
 # Install PM2 globally for process management with minimal footprint