Add lint workflow

[ediamin]

Summary

• remove Husky and lint-staged from the package setup
• add a dedicated GitHub Actions lint workflow for PHP, JS, CSS, package.json, and TypeScript checks
• shift lint enforcement from local git hooks to CI

Validation

• npm run lint:js
• npm run lint:css
• npm run lint:types
• npm run lint:pkg-json
• PHP lint checks could not be run locally because php is not installed on this machine; GitHub Actions will validate them