chore(HNT-3495): upgrade Node 18 to 24

[mmiermans]

Goal

Move admin-api to Node 24 (Active LTS). Apollo Server 5 requires Node ≥20, and the service runs Node 18 (EOL) in production and Node 16 in CircleCI.

• Dockerfile: node:18 → node:24 (digest-pinned)
• .nvmrc and the super-linter workflow: 18 → 24
• CircleCI build/test_specs: deprecated circleci/node:16.13.1 → cimg/node:24.21.0

Implementation Decisions

• Runtime and CI config only, with no dependency changes, so a deploy problem can be traced to the runtime alone. @types/node stays at 18 because the transitive TypeScript 4.7 can't parse the Node 24 types; the AS5 PR handles TypeScript.
• .aws/ (CDKTF) keeps its own Node version; it runs in CodeBuild, not in the service image.

Deployment steps

• Deploy to dev and check the ECS task is healthy
• Smoke-test an image upload and a query from the curation admin tools

References

JIRA ticket:

• HNT-3495 (part of HNT-1771)

Stacked on #390.