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/action-oriented.txt

@@ -0,0 +1,3 @@
+The plan is done. docs/plans/auth-system.md has everything.
+
+Do subagent-driven development on this - start with Task 1, dispatch a subagent, then we'll review.

tests/explicit-skill-requests/prompts/after-planning-flow.txt

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+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

tests/explicit-skill-requests/prompts/claude-suggested-it.txt

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+[Previous assistant message]:
+Plan complete and saved to docs/plans/auth-system.md.
+
+Two execution options:
+1. Subagent-Driven (this session) - I dispatch a fresh subagent per task, review between tasks, fast iteration within this conversation
+2. Parallel Session (separate) - Open a new Claude Code session with the execute-plan skill, batch execution with review checkpoints
+
+Which approach do you want to use for implementation?
+
+[Your response]:
+subagent-driven-development, please

tests/explicit-skill-requests/prompts/i-know-what-sdd-means.txt

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+I have my implementation plan ready at docs/plans/auth-system.md.
+
+I want to use subagent-driven-development to execute it. That means:
+- Dispatch a fresh subagent for each task in the plan
+- Review the output between tasks
+- Keep iteration fast within this conversation
+
+Let's start - please read the plan and begin dispatching subagents for each task.

tests/explicit-skill-requests/prompts/mid-conversation-execute-plan.txt

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+I have a plan at docs/plans/auth-system.md that's ready to implement.
+
+subagent-driven-development, please

tests/explicit-skill-requests/prompts/please-use-brainstorming.txt

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+please use the brainstorming skill to help me think through this feature

tests/explicit-skill-requests/prompts/skip-formalities.txt

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+Plan is at docs/plans/auth-system.md.
+
+subagent-driven-development, please. Don't waste time - just read the plan and start dispatching subagents immediately.

tests/explicit-skill-requests/prompts/subagent-driven-development-please.txt

@@ -0,0 +1 @@
+subagent-driven-development, please

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

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