Add GitHub Actions CI workflow

[benvinegar]

Summary

• add a GitHub Actions CI workflow for pull requests, pushes to main, and manual runs
• install dependencies with Bun 1.3.10 and validate formatting, lint, tests, and build
• disable Husky in CI to keep workflow setup deterministic

Validation

• bun run format:check
• bun run lint
• bun run test
• bun run build

This PR description was generated by Pi using GPT-5