Run linter in CI

[lornakelly]

Summary

Add a GitHub Actions workflow that runs the project linter on every Pull Request and blocks merges if linting fails, ensuring consistent code quality and formatting standards.

Goals

• Execute linting automatically on every PR.
• Fail CI if any linting errors occur.
• Reduce code review noise related to formatting and basic rule violations.

Non-Goals

• Auto-fixing lint issues in CI (developers fix locally).
• Enforcing coverage thresholds.
• Replacing unit tests or static security analysis (separate workflows).