Add pytest as a test dependency

[inayayousfi]

Problem

The test suite currently runs through python -m unittest discover -s tests, which works, but some runtime and Qt-oriented tests would be easier to express and maintain with pytest fixtures and assertion helpers.

Proposal

Add pytest as a development/test dependency and document the preferred test command. Keep existing unittest-compatible tests working unless there is a deliberate migration plan.

Potential Benefits

• Cleaner shared QApplication/Qt fixtures.
• Less boilerplate for runtime prompt/window tests.
• Easier parametrization for config-driven component behavior.
• More readable assertions while preserving the current test coverage.

Acceptance Criteria

• pytest is available in the documented development/test environment.
• The documented test command is updated if pytest becomes preferred.
• Existing tests continue to pass.
• Any migration from unittest style is incremental and does not block unrelated refactors.