Add comprehensive test coverage

[MartinPTielemans]

Description

The codebase currently has minimal test coverage. While there are some unit tests in src-tauri/src/command.rs, the frontend React components and most of the Rust backend functionality lack proper test coverage.

Areas needing tests:

Frontend (React/TypeScript)

• App.tsx component functionality
• UpdateChecker.tsx component behavior
• User interaction flows (PM selection, monitoring toggle)
• Error handling scenarios

Backend (Rust)

• Clipboard monitoring functionality
• Command translation logic (expand existing tests)
• Update checking and installation
• Tauri command handlers
• Error handling and edge cases

Suggested improvements:

1. Add frontend testing framework (Jest + React Testing Library)
2. Expand Rust unit tests with more edge cases
3. Add integration tests for clipboard monitoring
4. Add end-to-end tests for the full user workflow
5. Set up test coverage reporting

Benefits:

• Prevent regressions when adding new features
• Ensure reliability of clipboard monitoring
• Validate command translation accuracy
• Improve confidence in releases