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/after-planning-flow.txt

@@ -0,0 +1,17 @@
+Great, the plan is complete. I've saved it to docs/plans/auth-system.md.
+
+Here's a summary of what we designed:
+- Task 1: Add User Model with email/password fields
+- Task 2: Create auth routes for login/register
+- Task 3: Add JWT middleware for protected routes
+- Task 4: Write tests for all auth functionality
+
+Two execution options:
+1. Subagent-Driven (this session) - dispatch a fresh subagent per task
+2. Parallel Session (separate) - open new Claude Code session
+
+Which approach do you want?
+
+---
+
+subagent-driven-development, please