[WIP] Port JavaScript code to TypeScript with linter

[Copilot]

• Port eslint.config.js to TypeScript (eslint.config.ts)
• Update tsconfig.node.json to include eslint.config.ts
• Verify linter still works correctly
• Run build to ensure no issues
• Clean up old eslint.config.js file

Original prompt

Port the JavaScript code here to TypeScript. Maintain functionality, and ensure a typescript linter is introduced with a sensible set of defaults.

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