[Core] Comprehensive Testing Strategy

[seppelz]

Comprehensive Testing Strategy\n\n## Consolidated Issues\n- #33 QA Test Coverage Strategy\n- #52 Enhanced Test Coverage for Calendar Features\n- #18 Testing Strategy Implementation\n\n## Objectives\n1. Test Coverage Framework\n2. Calendar Feature Testing\n3. CI/CD Integration\n\n## Acceptance Criteria\n- Complete test coverage plan\n- Automated test suite\n- Calendar component tests\n- Integration tests\n- Performance testing\n- CI/CD pipeline integration\n\n## Technical Notes\n- Jest configuration\n- React Testing Library\n- E2E testing setup\n- Performance metrics