Integrate testing-skills-with-subagents into writing-skills

- Moved testing-skills-with-subagents to writing-skills/testing-skills-with-subagents.md
- Moved examples/ directory to writing-skills/examples/
- Updated writing-skills to reference via @testing-skills-with-subagents.md
- Updated README to reflect consolidation
- Removed standalone skill (now a supporting reference)

skills/writing-skills/SKILL.md

@@ -181,7 +181,7 @@ Use words Claude would search for:
 
 **Use active voice, verb-first:**
 - ✅ `creating-skills` not `skill-creation`
-- ✅ `testing-skills-with-subagents` not `subagent-skill-testing`
+- ✅ `condition-based-waiting` not `async-test-helpers`
 
 ### 4. Token Efficiency (Critical)
 
@@ -520,7 +520,7 @@ Run same scenarios WITH skill. Agent should now comply.
 
 Agent found new rationalization? Add explicit counter. Re-test until bulletproof.
 
-**REQUIRED SUB-SKILL:** Use superpowers:testing-skills-with-subagents for the complete testing methodology:
+**Testing methodology:** See @testing-skills-with-subagents.md for the complete testing methodology:
 - How to write pressure scenarios
 - Pressure types (time, sunk cost, authority, exhaustion)
 - Plugging holes systematically