[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 to require Node 18, note corepack transition, and refresh governance/CoC links and TSC meeting/contact info.

• Docs (CONTRIBUTING.md):
  • Bump Node.js requirement to >=18; clarify yarn usage with Volta and transition to Node corepack.
  • Refresh governance links: Technical Charter (CHARTER.md) and Governance (GOVERNANCE.md).
  • Update community info: TSC meets bi-weekly via Zoom; add OpenJS Slack; remove mailing list reference.
  • Switch Code of Conduct reference to OpenJS Foundation CPC link.

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[coveralls]

coverage: 91.144%. remained the same
when pulling 429500d on chr/contributing
into 9bfe769 on master.