Implement comprehensive test suite

## Description
Add comprehensive testing to ensure code quality and reliability.

## Tasks
- [ ] Unit tests for Go API (80%+ coverage)
- [ ] Unit tests for Python enrichment service
- [ ] Unit tests for React components
- [ ] Integration tests for API endpoints
- [ ] End-to-end tests for critical user flows
- [ ] Performance tests for high-load scenarios
- [ ] Security tests for authentication and authorization

## Acceptance Criteria
- [ ] All new code has corresponding tests
- [ ] Test coverage exceeds 80%
- [ ] All tests pass in CI/CD pipeline
- [ ] Performance benchmarks are established

## Priority: High
**Type**: Feature
**Component**: Testing
**Estimated Effort**: 2-3 weeks

Begin by mapping the Go API, Python enrichment service, and React components, then identify the API endpoints and critical user flows that need coverage. Establish coverage across unit, integration, end-to-end, performance, and security tests; done means 80%+ coverage, passing CI/CD tests, and established performance benchmarks.

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