test: migrate from Jest to Vitest (Phase 1 complete)

- Remove Jest and all related packages
- Install Vitest with coverage support
- Create vitest.config.ts with path aliases
- Set up global test configuration
- Migrate all 6 test files to Vitest syntax
- Update TypeScript configuration for better Vitest support
- Create separate tsconfig.build.json for clean builds
- Fix all import/module issues in tests
- All 68 tests passing successfully
- Current coverage baseline: 2.45%

Phase 1 of testing suite improvement complete.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

docs/testing-checklist.md

@@ -4,12 +4,22 @@
 
 - [x] ~~Fix failing tests (Phase 0)~~ ✅ COMPLETED
 - [x] ~~Create GitHub Actions workflow file~~ ✅ COMPLETED
-- [ ] Install Vitest and remove Jest
-- [ ] Create vitest.config.ts
-- [ ] Setup global test configuration
-- [ ] Migrate existing tests to Vitest syntax
+- [x] ~~Install Vitest and remove Jest~~ ✅ COMPLETED
+- [x] ~~Create vitest.config.ts~~ ✅ COMPLETED
+- [x] ~~Setup global test configuration~~ ✅ COMPLETED
+- [x] ~~Migrate existing tests to Vitest syntax~~ ✅ COMPLETED
 - [ ] Setup coverage reporting with Codecov
 
+## Phase 1: Vitest Migration ✅ COMPLETED
+
+All tests have been successfully migrated from Jest to Vitest:
+- ✅ Removed Jest and installed Vitest
+- ✅ Created vitest.config.ts with path aliases
+- ✅ Set up global test configuration
+- ✅ Migrated all 6 test files (68 tests passing)
+- ✅ Updated TypeScript configuration
+- ✅ Cleaned up Jest configuration files
+
 ## Week 1: Foundation
 
 ### Testing Infrastructure