Add ESLint workflow for code quality enforcement

[mcpdev0910]

Summary

This PR adds a comprehensive ESLint workflow to enforce code quality standards across the repository. The setup includes:

• ESLint configuration with recommended rules
• GitHub Actions workflow that runs on all pushes to main and pull requests
• Enforcement of coding standards including unused variables, console usage, semicolons, and quotes

Changes

• .eslintrc.json - ESLint configuration file with custom rules
• .github/workflows/lint.yml - GitHub Actions workflow for automated linting
• src/example.js - Example file with intentional linting errors to demonstrate the workflow

Testing

The workflow can be tested by:

1. Creating a PR with JavaScript files that violate the linting rules
2. Observing the GitHub Actions workflow fail when linting errors are present
3. Fixing the linting errors and seeing the workflow pass

Note: This PR intentionally includes linting errors in src/example.js to demonstrate the workflow functionality. These errors will be fixed in a subsequent commit.