[pstamatop]

Summary

Establish a clean ESLint baseline and enforce it through pre-commit and CI.

• Configure ESLint’s and typescript-eslint’s recommended presets for source and config files
• Enable Vitest’s recommended ESLint rules for test files.
• Resolve existing violations through const conversions, unused-code cleanup and minor test adjustments.
• Preserve existing types to avoid mixing a typing refactor into the ESLint setup, use _ for intentionally unused names.
• Add yarn lint with zero warnings allowed, a pre-commit hook and a Node 24 CI job.

Testing

• Run yarn lint with 0 errors and 0 warnings
• Run yarn test with 106 successful tests
• eslint pre-commit hook passes

Before submitting

• I have read the Contribution Guidelines.