Add ESLint and Prettier for consistent code style

[ShivamH1]

Closes #165

What

Adds ESLint and Prettier to enforce consistent code style across the codebase.

Why

No linting or formatting tools were configured. Code style was enforced through convention only, making it easy for inconsistencies to slip into PRs.

Changes

• Add .eslintrc.json with @typescript-eslint/recommended + prettier config
• Add .prettierrc matching existing codebase conventions
• Add .prettierignore to exclude build output
• Add lint, lint:fix, format, format:check scripts to package.json
• Add ESLint and Prettier devDependencies
• Format all TypeScript files with Prettier
• Fix minor lint issues (unused vars, empty interface, eslint-disable for intentional patterns)

Verification

• npm run lint — 0 errors, 3 warnings
• npm run format:check — all files pass
• npm test — all tests pass