chore: upgrade Node.js 20 (EOL) → 24 LTS

[islandbitcoin]

Summary

Node.js 20 reached end-of-life in April 2026. This bumps the project to Node 24 (LTS, supported through ~April 2028).

Changes by category

• package.json engines — >=20.18.1 <21 → >=24.0.0 <25
• @types/node — ^20.6.2 → ^24 (resolves to 24.13.2 in yarn.lock)
• 4 Dockerfiles — Dockerfile, Dockerfile-debug, Dockerfile-migrate, Dockerfile-websocket: node:20-alpine → node:24-alpine; distroless nodejs20-debian11 → nodejs24-debian12 (incl. :debug tag)
• 9 GitHub Actions workflows — node-version: 20 → 24 (bats, check-code, integration-test, audit, mongodb-migrate, generate-graphql-docs, unit-test, vendor/nodejs-audit, vendor/nodejs-check-code)
• flake.nix — nodejs_20 → nodejs_24 (overlay + yarn override)
• DEV.md — Node version references updated to 24; corrected the stale "Node 22+ breaks yarn install" warning (see below)
• tsconfig.json — added "lib": ["es2022"] (required after the @types/node@24 bump; see below)
• src/utils/grpc-stream-client/stream.ts — replaced as AddEventListenerOptions (a DOM type no longer in scope) with an inline { once?: boolean } cast

Validation (run under Node v24.18.0)

• yarn install — passed, exit 0 (the repo's .yarnrc has ignore-engines true, so engine checks are bypassed). The old DEV.md claim that "Node 22+ will fail on yarn install" did not hold true under Node 24; the warning has been corrected.
• yarn build (tsconfig-build.json, the production build) — passed, exit 0.
• yarn tsc-check — the @types/node@24 bump initially surfaced 2 new type errors (Array.prototype.at() needing es2022 lib, and a removed AddEventListenerOptions DOM type). Both are fixed by the tsconfig.json lib addition and the inline cast. The remaining tsc-check failures are pre-existing errors in test/flash/integration/** spec files (verified identical on main under Node 20) and are unrelated to this upgrade.

Distroless image note

Verified gcr.io/distroless/nodejs24-debian12 exists via docker manifest inspect (OK). nodejs24-debian11 does not exist (MISSING), so all distroless references use debian12.

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