chore: add ESLint quality gate

[floze-the-genius]

Summary

• add ESLint flat config with the recommended JavaScript and TypeScript rule sets
• add npm run lint and run it in the existing Node 20/22 CI matrix
• remove one unused test helper binding surfaced by the new gate

The config keeps existing any, dynamic require, intentional empty catches, and current assignment patterns as explicit legacy baselines. This avoids broad unrelated source churn while still making the remaining recommended rules enforceable for new changes.

Closes #50

Validation

• npm run lint
• npm run typecheck
• npm test — 120/120 passed
• npm run build
• npm pack --dry-run
• npm audit — 13 existing advisories on both current main and this PR; no new advisory delta
• git diff --check

All commands passed on Node.js 22.23.1. The lockfile uses patched brace-expansion 5.0.9, avoiding the extra high advisory present in 5.0.7.

Screenshots

Not applicable; this change only affects development tooling and CI.

[floze-the-genius]

@kannupriyakalra This remains one current commit for your good-first issue #50. I refreshed the lockfile to patched brace-expansion 5.0.9 so the ESLint tooling adds no audit delta versus main (13 existing advisories on both). Fresh lint, typecheck, 120/120 tests, build, npm pack, audit comparison, and diff check pass on Node 22.23.1. The new Node 20/22 CI run is stopped at action_required before jobs start. Could you approve the workflow and review when convenient?