chore: Add tests and improve code coverage.

.github/CI_QUICK_REFERENCE.md

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+# Quick CI Reference
+
+## What Runs on Push/PR
+
+```bash
+1. npm run lint              # Code style check
+2. npm run test:coverage     # Run all 169 tests
+3. Coverage check ≥ 90%      # Enforce threshold
+4. npm run build             # Build verification
+```
+
+## CI Status Meanings
+
+- ✅ **Green Check** - All passed, ready to merge
+- ❌ **Red X** - Failed, needs fixing
+- 🟡 **Yellow Dot** - Running, please wait
+- ⚪ **Gray Dot** - Queued or skipped
+
+## Quick Fixes
+
+### Lint Failed
+```bash
+npm run lint:fix
+git add .
+git commit -m "fix: lint errors"
+git push
+```
+
+### Tests Failed
+```bash
+npm test
+# Fix the failing tests
+git add .
+git commit -m "fix: failing tests"
+git push
+```
+
+### Coverage < 90%
+```bash
+npm run test:coverage
+# Check coverage/index.html
+# Add tests for uncovered lines
+git add .
+git commit -m "test: increase coverage"
+git push
+```
+
+### Build Failed
+```bash
+npm run build
+# Fix TypeScript errors
+git add .
+git commit -m "fix: build errors"
+git push
+```
+
+## Local Pre-Push Checklist
+
+```bash
+✓ npm run lint              # Passes?
+✓ npm run test:coverage     # All green?
+✓ Coverage ≥ 90%?           # Check report
+✓ npm run build             # Compiles?
+```
+
+If all ✓, you're good to push! 🚀
+
+## View CI Results
+
+- **PR Page** - See check status at bottom
+- **Actions Tab** - View detailed logs
+- **Artifacts** - Download coverage reports
+
+## CI Workflow Location
+
+`.github/workflows/ci.yml`
+
+## Need Help?
+
+See [CI Setup Guide](.github/CI_SETUP.md) for detailed information.
+