Convert disabled real-injection tests to proper unit tests

[Coldaine]

Issue Description

The real injection tests are currently disabled in src/tests/real_injection.rs.disabled and need to be converted to proper unit tests that can run reliably in CI.

Current State

• Real injection tests exist but are disabled (src/tests/real_injection.rs.disabled)
• Tests require GUI applications and real display servers
• Currently not run in CI/CD pipeline

Requirements

1. Convert disabled integration tests to unit tests using mocks
2. Create test applications that can run in headless environments
3. Ensure tests don't require real hardware/environment access
4. Enable comprehensive testing without security/performance concerns

Benefits

• Better CI reliability
• More comprehensive code coverage
• Easier to catch regressions in real-world scenarios
• Improved developer experience

[google-labs-jules]

Jules is on it. When finished, you will see another comment and be able to review a PR.

[google-labs-jules]

Ready for a review! A PR has been created.