ci: verify supported Node runtimes

[rogerchappel]

Summary

• run repository hygiene and the complete release check on Node.js 20, 22, and 24 with independent matrix results
• add a regression contract tying CI coverage to the package engine floor and supported majors
• document the tested runtime policy in the release-readiness guidance

Commits

• 1b479c4 test: enforce supported Node CI matrix
• b9deae6 ci: verify supported Node runtimes
• 696486b docs: describe CI runtime coverage

Verification

• npm ci
• npm run release:check (28 tests, typecheck, build, CLI smoke, package consumer smoke)
• git diff --check origin/main...HEAD
• author and committer identity verified for every proposed commit as Roger Chappel <miscanalysis@gmail.com>

[rogerchappel]

Automated merge note

Triage class: auto-merge

Summary: Adds Node 20/22/24 CI coverage, a workflow-matrix contract test, and README coverage documentation.

Checks run: Repository hygiene (Node 20) — SUCCESS; Repository hygiene (Node 22) — SUCCESS; Repository hygiene (Node 24) — SUCCESS. Branch protection verified: one approving review required; no required status checks.

Rebased/CI-repaired: no.

Verified head SHA: 696486b.