Modernize Node/npm setup: switch workflows to latest Node, centralize legacy peer deps, and align React type packages

[Copilot]

This PR updates repository/tooling configuration to use the latest Node runtime in CI, removes scattered --legacy-peer-deps flags by centralizing the setting in .npmrc, and upgrades React type package ranges to ^18.0.0.

• CI runtime updates

  • Replaced node-version: "20.9.0" with node-version: "latest" across all GitHub Actions workflows that set up Node:
    • deploy.yml
    • update-from-issue.yml
    • update-from-csv.yml (both jobs)
    • patch-from-csv.yml
    • copilot-setup-steps.yml

• npm peer-deps behavior centralized

  • Added root .npmrc:

    legacy-peer-deps=true

  • Removed explicit --legacy-peer-deps flags from workflow commands and package scripts (including iw in package.json), so installs/builds rely on repo-level npm config instead of per-command flags.

• React type definitions aligned to React 18

  • Updated package.json:
    • @types/react → ^18.0.0
    • @types/react-dom → ^18.0.0
  • Regenerated lockfile entries to reflect the new ranges.

• Docs/config references cleaned up

  • Updated install/runtime guidance in:
    • README.md
    • .github/copilot-instructions.md
  • Removed references instructing use of --legacy-peer-deps directly.

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