platform: drop EOL Node 18 from engines, add Nuxt engines, test 22+24, pin publish (#174)

[IgorShevchik]

Closes #174.

The SDK advertised runtimes it never tested (including two EOL lines) and built the published artifact on a floating lts/* that CI never validated — silent compatibility drift in both directions.

Changes (non-breaking hygiene)

The genuinely breaking move — dropping Node 20 — is deferred to the next major and tracked in #312.

• packages/jssdk engines: ^18.0.0 || ^20.0.0 || >=22.0.0 → ^20.0.0 || >=22.0.0 (drop EOL Node 18).
• packages/jssdk-nuxt: add engines.node: "^20.0.0 || >=22.0.0" (it had none).
• ci.yml test job: run the unit suite on a Node 22 + 24 matrix (fail-fast: false) so the advertised runtimes are actually exercised. The node-agnostic pnpm audit is gated to the 22 leg so it still runs exactly once.
• Both npm-publish workflows: pin node-version from floating lts/* → 22 — the lowest supported + CI-validated line, so the published artifact is built on the floor (consumable by every supported consumer) with a deterministic runtime.

Docs / consistency synced

The engines string in 4.nodejs.md, the "Node.js 18+" floor in 12 example pages, README-AI.md, the b24jssdk-core skill, and the local docker-compose.yml smoke matrix (test-node18/20 → 22/24) all now reflect the supported set. CHANGELOG.md [Unreleased] › Changed records the drop.

Why pin publish to 22 (not 24)

The artifact should build on the lowest runtime we still support and validate, not the newest — so nothing that only breaks on an older-but-supported runtime slips through. Both 22 and 24 are now in CI; 22 is the conservative, fully-validated choice. (lts/* currently resolves to 24, so this also removes the float.)

Known gap (tracked)

engines still advertises Node 20 (EOL) but CI tests only 22 + 24 — adding a soon-to-be-removed line to the matrix wasn't worth the runner minutes. The gap is closed by removing 20 in #312, not by growing the matrix backward.

Verification

• pnpm --filter @bitrix24/b24jssdk typecheck — clean · pnpm run lint — 0 errors
• pnpm run package-jssdk:test:run-unit — 377 passed
• pnpm run lint:md — 0 errors · node scripts/docs-lint.mjs --strict — 0/0
• All 3 workflow YAMLs + both package.json parse clean

Reviewed by a 5-perspective pass (CI-correctness, platform/semver, docs/consistency, supply-chain/publish, tech-director). Their findings are folded in: publish pinned to 22 (tech-director), the CHANGELOG entry added (all), and 3 doc stragglers fixed (docs reviewer: README-AI.md, SKILL.md, docker-compose.yml).

Note on required checks: this turns test into test (22) / test (24). The required status check is the ci aggregator (which contains(needs.*.result, 'failure') across matrix legs), so this doesn't affect branch protection.

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