Add CI Pipeline and UI Background Colors

[VivaciousEmu]

Changes Included:

• ✅ Implemented GitHub Actions CI/CD pipeline (.github/workflows/ci.yml)
• ✅ Added automated build, test, and packaging with Maven
• ✅ Configured artifact upload for test reports and JAR files
• ✅ Enhanced UI with background colors on all screens (login, user creation, main interface)

Verification:

• All GitHub Actions workflows are passing
• Application builds successfully with mvn clean package
• Unit tests are executed automatically
• JAR artifacts are generated and available for download