Drop Node 20 support and refresh dependency stack

[Conalh]

Summary

• raise the package runtime floor from Node >=20 to Node >=22
• move CI from Node 20/22 to Node 22/24 and update checkout/setup-node actions
• upgrade the compatible dependency set together: agent-gov-core 1.4, Ink 7.1, React 19.2, @types/react 19.2
• ignore semver-major TypeScript/@types-node dependabot updates for now so compiler-major work stays separate

Verification

• npm ci
• npm test
• node dist/cli.js --help
• npx -y node@22 --version
• npx -y node@22 dist/cli.js --help
• npx -y node@22 --test

Supersedes dependabot PRs #13, #18, #20, #21, and #22. PR #14 remains a separate TypeScript 6 / @types-node major migration and should be closed/deferred by this Dependabot rule.

[Conalh]

Follow-up: Windows Node 24 hit a native recursive fs.watch assertion in CI. This branch now routes Windows Node 24+ through the existing polling fallback while keeping the recursive watcher on Windows Node 22.