Update "tdd" skill description to match documented workflow

The "tdd" skill description currently says: «"Use when the user wants to build features or fix bugs test-first, mentions 'red-green-refactor'..."» However, the skill documentation explicitly states that refactoring is not part of the loop: «"Refactoring is not part of the loop. It belongs to the review stage..."» To keep the documentation internally consistent, the description should be updated so it no longer refers to "red-green-refactor" unless the skill is intended to document the refactor phase as well. For example, the description could instead say: «"Test-driven development. Use when the user wants to build features or fix bugs test-first."» or otherwise describe the workflow in a way that matches the rest of the document.