[docs] Revise Node.js version and governance references

[chrisgervang]

Updated Node.js version requirement based on version pinned with Volta, and governance links. Also mention we're transitioning to Node corepack since we have packageManager in our package.json

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Note

Updates CONTRIBUTING.md to require Node.js >=18, note yarn management via Volta/Corepack, and refresh governance, meeting, and Code of Conduct links.

• Docs (CONTRIBUTING.md):
  • Dev environment:
    • Bump Node.js requirement to >=18.
    • Clarify yarn management: still using Volta; transitioning to Node corepack.
  • Governance:
    • Update links to CHARTER.md and GOVERNANCE.md.
    • Replace TSC meeting info with bi-weekly Open Visualization meeting (Zoom) and add #deckgl on OpenJS Slack.
  • Code of Conduct:
    • Switch reference to OpenJS CPC CODE_OF_CONDUCT.md.

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[coveralls]

coverage: 91.144%. remained the same
when pulling 81cd0e7 on chr/contributing
into 8549120 on master.