Migrate from CommonJS to ESM

[JiwaniZakir]

Problem

The project uses CommonJS require() throughout 40+ source files. Modern Node.js 20+ has stable ESM support and many dependencies are moving ESM-only.

Proposed Solution

• Add "type": "module" to package.json
• Convert require() calls to import statements
• Convert module.exports to export statements
• Update Jest config to support ESM (or migrate to Vitest)
• This is a larger refactor — could be done incrementally per directory