Align runtime to Node 20 LTS and enforce version via engines/.nvmrc; update README #1182
Description
README states Node 16 (Gallium), but repo uses Yarn Berry (v4), @types/node@20, and node --test which requires Node 18+. Running with Node 16 can currently throw a Corepack URL.canParse error if the environment isn’t set up consistently.
Proposed changes:
- Update README to require Node 20.x LTS (Iron).
- Add .nvmrc with 20.x (e.g., 20.19.0)
- Add engines to package.json and .npmrc with engine-strict=true.
- Add README setup steps: corepack enable and yarn --version sanity check.
Rationale: Prevents toolchain drift and avoids Corepack/Yarn mismatch. Matches TypeScript types and built-in test runner.
