docs: update CONTRIBUTING.md and README contribute section

[jordan-a-young]

What was stale

README.md

• Node version said v24 only — engines and CI matrix both support v22 and v24
• npm i -g yarn (missing npm install form) and no mention of Corepack as the recommended activation path for yarn v4
• No Contributing section pointing contributors to the guide

CONTRIBUTING.md

• npm -i -g yarn — wrong flag (-i is not valid here)
• Node version said v24 only — CI runs on both 22 and 24
• No mention of Corepack or how yarn v4 actually activates
• No Prerequisites section
• No step-by-step contributor workflow (fork → clone → install → change → test → commit → PR)
• yarn vitest packages/alert shown as watch mode — wrong; corrected to yarn vitest --watch packages/alert
• yarn lint not documented — only lint:affected was shown
• No Versioning and Releases section explaining the automated release flow via CI
• No note that docs commits do not trigger a version bump
• test:affected script not documented

What was checked / not changed

• @jscutlery/semver config: all 54 project.json files already have "skipCommitTypes": ["docs"] — no change needed
• All documented scripts were verified to exist in package.json
• No scripts invented — everything in the updated docs is backed by actual package.json entries or CI config

Files changed

• README.md — node version, Corepack instructions, Contributing section
• .github/CONTRIBUTING.md — prerequisites, contributor workflow, corrected commands, versioning section, docs commit note

[github-actions]

🚀 Preview deployed!

📖 View Storybook Preview