Strengthen using-superpowers for explicit skill requests

Addresses failure mode where Claude skips skill invocation even when
user explicitly requests it by name (e.g., "subagent-driven-development,
please").

Skill changes:
- "Check for skills" → "Invoke relevant or requested skills"
- "BEFORE ANY RESPONSE" → "BEFORE any response or action"
- Added reassurance that wrong skill invocations are okay
- New red flag: "I know what that means"

Tests:
- New test suite for explicit skill requests
- Single-turn and multi-turn scenarios with --continue
- Tests with haiku model and user CLAUDE.md

tests/explicit-skill-requests/prompts/use-systematic-debugging.txt

@@ -0,0 +1 @@
+use systematic-debugging to figure out what's wrong