test: implement frontend test coverage enforcement with CI integratio…

[Uyoxy]

Overview

Implements frontend test coverage enforcement for UI components and critical logic.

Implementation

• Configured Jest/Vitest with React Testing Library
• Added test utilities setup
• Implemented coverage reporting
• Added coverage threshold enforcement
• Integrated tests into CI pipeline
• Prevented merge if coverage drops

Tests Added

• Component rendering tests
• User interaction tests
• Loading states
• Error states

Configuration Updates

• jest.config.ts / vitest.config.ts
• package.json scripts
• test/utils setup files

Result

• Coverage thresholds enforced
• CI fails when coverage drops
• Critical UI flows protected from regressions

Closes #71