Add testing setup, prettier config and CI workflow

[jupier]

 This PR adds:
 - Jest/Vitest testing setup with example component tests
 - Prettier configuration with standard settings
 - GitHub Actions CI workflow for automated testing
 - .nvmrc for Node version management (v20.11.1)
 
 The CI workflow will:
 - Check code formatting
 - Run ESLint
 - Run tests
 - Build the project