Add Jest as dev dependency

[SeanChen327]

Pull Request Review Checklist

Code Quality

• Code follows project style guidelines (Google Java Style for backend, ESLint/Prettier for frontend)
• Code is readable, maintainable, and uses clear naming
• No unnecessary or commented-out code

Functionality

• Code runs as intended and solves the issue/feature described
• No breaking changes introduced without justification
• Input validation and error handling are in place

Testing

• Unit tests or integration tests cover new/changed logic
• All existing tests pass
• Manual testing steps (if any) are described in the PR

Security & Stability

• No secrets, credentials, or sensitive data committed
• SQL queries, API calls, or file operations are safe from injection or misuse
• Dependencies added are necessary and from trusted sources

Project Process

• Branch name and commit messages follow team conventions
• PR is scoped to a single feature or fix (not overloaded)
• Documentation, comments, or README updates provided if needed

[prlara23Pro]

LGTM