[CI] 🧪 Add frontend test coverage

[ahmdkaml]

🧪 Problem

The React frontend currently has no test files or test coverage.

The CI workflow can verify that the frontend builds successfully, but it does not currently verify application behavior.

🎯 Goal

Introduce a frontend testing setup and establish an initial test suite for the React application.

The tests should provide a reliable baseline that can be expanded as the frontend develops.

✅ Acceptance Criteria

• A frontend test framework is configured
• Initial tests are added for the React application
• Tests run successfully locally
• Tests run successfully in CI
• CI fails when a frontend test fails
• The test setup works with the existing React + Vite + TypeScript configuration
• Initial test coverage is documented

📌 Scope

This issue is focused on establishing the testing foundation and baseline coverage.

It does not require comprehensive coverage of every component or feature.