Add basic test infrastructure with Jest and React Testing Library

[Copilot]

This PR adds a minimal testing setup to the project to establish a foundation for future test development.

Changes Made

• Test Infrastructure: Added Jest configuration with Next.js integration and React Testing Library
• Test Dependencies: Installed jest, @testing-library/react, @testing-library/jest-dom, and jest-environment-jsdom
• Configuration Files:
  • jest.config.mjs - Jest configuration with Next.js support
  • jest.setup.js - Test setup file with jest-dom matchers
• Test Scripts: Added test and test:watch scripts to package.json
• Sample Tests: Created basic tests to demonstrate the setup:
  • src/__tests__/utils.test.ts - Tests for formatBytes and formatDate utility functions
  • src/__tests__/button.test.tsx - Tests for the Button component
• Documentation: Updated README.md with testing instructions

Test Coverage

The initial tests cover:

• Utility functions (formatBytes, formatDate) with various edge cases
• UI component (Button) with different variants, sizes, and states
• All 9 tests are passing successfully

Usage

# Run tests once
npm test

# Run tests in watch mode
npm run test:watch

This provides a solid foundation for adding more comprehensive tests as the project grows.

Fixes #62.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• fonts.googleapis.com
  • Triggering command: node /home/REDACTED/work/cloudnet-webinterface/cloudnet-webinterface/node_modules/.bin/next build (dns block)
• o1.ingest.sentry.io
  • Triggering command: node /home/REDACTED/work/cloudnet-webinterface/cloudnet-webinterface/node_modules/.bin/next build (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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