fix(skills): broaden writing-good-tests trigger to any test writing

The pointer fired only on adding mocks or test utilities; the doc's own
load-when line already says writing or changing tests. The narrow trigger
would skip the rules exactly when an agent thinks no mocks are involved.

skills/test-driven-development/SKILL.md

@@ -203,7 +203,7 @@ Next failing test for next feature.
 | **Clear** | Name describes behavior | `test('test1')` |
 | **Shows intent** | Demonstrates desired API | Obscures what code should do |
 
-When adding mocks or test utilities, read [writing-good-tests.md](writing-good-tests.md) for the rules that keep tests honest:
+When writing or changing any test, read [writing-good-tests.md](writing-good-tests.md) for the rules that keep tests honest:
 - Assert on real behavior, never on mock behavior
 - Keep test-only code in test utilities, out of production classes
 - Understand a dependency's side effects before mocking it