Add skill triggering test framework

Creates tests/skill-triggering/ to validate skills trigger correctly from
naive prompts (without explicitly naming the skill). Tests 6 skills:
- systematic-debugging
- test-driven-development
- writing-plans
- dispatching-parallel-agents
- executing-plans
- requesting-code-review

All 6 tests pass - skills trigger correctly based on their descriptions.

tests/skill-triggering/prompts/writing-plans.txt

@@ -0,0 +1,10 @@
+Here's the spec for our new authentication system:
+
+Requirements:
+- Users can register with email/password
+- Users can log in and receive a JWT token
+- Protected routes require valid JWT
+- Tokens expire after 24 hours
+- Support password reset via email
+
+We need to implement this. There are multiple steps involved - user model, auth routes, middleware, email service integration.