feat: add CI workflow with quality gates

[omachala]

Summary

• Add GitHub Actions CI workflow that runs on PRs and pushes to main
• Checks: Prettier, ESLint, TypeScript, Tests with 80% coverage threshold
• Add @vitest/coverage-v8 dev dependency for coverage reporting
• Branch protection updated to require "Check" status to pass

Checks performed

1. pnpm format:check - Prettier formatting
2. pnpm lint - ESLint
3. pnpm typecheck - TypeScript compilation
4. vitest run --coverage - Tests with coverage
5. Coverage threshold check (80% minimum)

Test plan

• Verify workflow runs on this PR
• Verify all checks pass
• Verify coverage threshold is enforced

[changeset-bot]

⚠️ No Changeset found

Latest commit: fbf942d

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR