Fix shallow testing issue: validate Action functionality instead of just checking method existence — a GitHub Copilot (GitHub) bot flight

From the pull request description

The tests in `test_gameplay_controller.py` only checked for `__init__` method existence (specifically `execute` method) without validating that the method actually works or that the class can be instantiated properly. This created shallow tests that could pass even if the Action class was broken or …

Excerpt (first 300 characters) — the full description is on GitHub.