Implement Comprehensive Unit Test Suite

[FJiangArthur]

Priority: High
Phase: 7
Estimate: 6 story points

Description:
Create comprehensive unit test suite covering all services and core functionality with >90% code coverage.

Current Issues:

• Many test files exist but have incomplete implementations
• Test coverage is insufficient for production quality
• Mock implementations need completion
• Integration between tests and actual code needs verification

Acceptance Criteria:

• >90% unit test coverage across all services
• All critical user workflows have test coverage
• Mock implementations are complete and realistic
• Tests run reliably in CI/CD environment
• Test documentation explains testing approach

Implementation Location:
Various test files in test/unit/services/ and test/