Update infrastructure dependencies for v2026.4

[matthew-white]

Update any dependencies other than Central Backend, Central Frontend, and Web Forms that need to be updated:

• ⚠️ Observe a 14-day dependency cooldown. Don't update to a Docker image that is newer than that unless there is a specific reason that's been discussed.
• Node in prod
  • Look at release schedule and make sure we're using an active LTS major version
  • Pin major, minor and patch releases
  • Related: pin npm versions with volta #2095
  • Update in:
    • service
    • nginx
    • secrets
• Node in dev
  • central-backend
  • central-frontend
    • Update for Web Forms packages as well (source)
• nginx-certbot in prod
  • Pin major and minor for both certbot and nginx
• nginx in central-frontend
  • Procfile
  • Match the version used in prod
• Postgres in prod
  • Related: Update postgres to v18 #1385
• Postgres in central-backend
  • test/bin/docker-postgres.sh
  • Match the version used in prod
• SMTP
• Enketo
• Redis
• pyxform-http
• npm dependencies in test/ directory of central repo

[matthew-white]

FYI @sadiqkhoja, I've updated the checklist above based on discussion at getodk/central-backend#1941 (comment). I added items related to updating Docker images in dev:

• nginx in central-frontend
• Postgres in central-backend

Let me know if it'd be helpful for me to file a separate issue about these or if you think we should be taking a different approach to updating these images.