Add Node.js 24 support, update minimum to Node 16+

[oligirling]

Summary

• Update Dockerfile from node:22-slim to node:24-slim
• Update CI matrix to test against Node.js 16, 18, 20, 22, and 24
• Update GitHub Actions to latest versions (checkout@v4, setup-node@v4)
• Add engines field in package.json requiring Node.js >=16.0.0
• Bump package version to 1.2.0
• Update README prerequisites to reflect Node 16+ support
• Add CHANGELOG.md

Test plan

• All 39 tests pass with 100% coverage on Node 24 (verified in Docker)
• CI should pass across Node 16, 18, 20, 22, and 24
• Verify npm publish works after merge

🤖 Generated with Claude Code

[coveralls]

Pull Request Test Coverage Report for Build 21980600268

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 11194461012:	0.0%
Covered Lines:	72
Relevant Lines:	72

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💛 - Coveralls