refactor(skills): reframe testing-anti-patterns as writing-good-tests

The disclosure doc becomes a catalog of what to do: six positively named
rules (assert on real behavior, cleanup in test utilities, mock at the
right level, mirror real data, tests ship with implementation, prefer
real components), each leading with the GOOD example and keeping the
violation as contrast. Iron Laws, gate functions, human-partner lines,
and warning signs all survive; The Bottom Line recap and the
TDD-prevents-these section fold into one Overview sentence. SKILL.md's
pointer moves into the Good Tests section it belongs with. Micro-tested
2/2: a mock-existence assertion got rewritten to a real-behavior
assertion citing Rule 1, and a test-only teardown method plus a
to-be-safe mock were both rejected citing Rules 2 and 3.

skills/test-driven-development/SKILL.md

@@ -203,6 +203,11 @@ 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:
+- 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
+
 ## Why Order Matters
 
 **"I'll write tests after to verify it works"**
@@ -354,13 +359,6 @@ Bug found? Write failing test reproducing it. Follow TDD cycle. Test proves fix
 
 Never fix bugs without a test.
 
-## Testing Anti-Patterns
-
-When adding mocks or test utilities, read [testing-anti-patterns.md](testing-anti-patterns.md) to avoid common pitfalls:
-- Testing mock behavior instead of real behavior
-- Adding test-only methods to production classes
-- Mocking without understanding dependencies
-
 ## Final Rule
 
 ```