Add comprehensive test suite (currently zero tests)

[StencilwashCoder]

Problem

Zero tests in the entire codebase. package.json confirms:

"test": "echo \"No tests yet\" && exit 0"

This is a financial supply chain app handling:

• Worker payroll via Lightning Network
• Coffee lot custody transfers
• QR-based attendance tracking

A bug could literally cost people money or lose coffee traceability data.

What Needs Testing

Unit Tests (Jest)

• utils/api.ts - All API functions with mocked fetch
• theme.ts - Color/spacing constants exist
• Component rendering - Button, Card, Header, etc

Integration Tests

• Worker flow: Login -> Scan QR -> Check-in confirmed
• Foreman flow: Create shift -> Generate QR -> Close shift
• Farm owner flow: Create lot -> Add weight -> GPS captured

E2E Tests (Detox/Maestro)

• Full worker check-in flow
• Camera permission handling
• Offline -> Online sync

Suggested Test Setup

# Add testing deps
npm install --save-dev jest @testing-library/react-native @testing-library/jest-native nock

# Add to package.json
"scripts": {
  "test": "jest",
  "test:watch": "jest --watch",
  "test:coverage": "jest --coverage"
}

Acceptance Criteria

• 80%+ code coverage on business logic (utils/api.ts)
• All API error paths tested
• QR scanning logic tested with mocked camera
• Payment/payroll calculation edge cases covered