Initial commit: Superpowers plugin v1.0.0

Core skills library as Claude Code plugin:
- Testing skills: TDD, async testing, anti-patterns
- Debugging skills: Systematic debugging, root cause tracing
- Collaboration skills: Brainstorming, planning, code review
- Meta skills: Creating and testing skills

Features:
- SessionStart hook for context injection
- Skills-search tool for discovery
- Commands: /brainstorm, /write-plan, /execute-plan
- Data directory at ~/.superpowers/

skills/collaboration/brainstorming/SKILL.md

@@ -0,0 +1,56 @@
+---
+name: Brainstorming Ideas Into Designs
+description: Interactive idea refinement using Socratic method to develop fully-formed designs
+when_to_use: When your human partner says "I've got an idea", "Let's make/build/create", "I want to implement/add", "What if we". When starting design for complex feature. Before writing implementation plans. When idea needs refinement and exploration. ACTIVATE THIS AUTOMATICALLY when your human partner describes a feature or project idea - don't wait for /brainstorm command.
+version: 2.0.0
+---
+
+# Brainstorming Ideas Into Designs
+
+## Overview
+
+Transform rough ideas into fully-formed designs through structured questioning and alternative exploration.
+
+**Core principle:** Ask questions to understand, explore alternatives, present design incrementally for validation.
+
+**Announce at start:** "I'm using the Brainstorming skill to refine your idea into a design."
+
+## The Process
+
+### Phase 1: Understanding
+- Check current project state in working directory
+- Ask ONE question at a time to refine the idea
+- Prefer multiple choice when possible
+- Gather: Purpose, constraints, success criteria
+
+### Phase 2: Exploration
+- Propose 2-3 different approaches (reference skills/coding/exploring-alternatives)
+- For each: Core architecture, trade-offs, complexity assessment
+- Ask your human partner which approach resonates
+
+### Phase 3: Design Presentation
+- Present in 200-300 word sections
+- Cover: Architecture, components, data flow, error handling, testing
+- Ask after each section: "Does this look right so far?"
+
+### Phase 4: Worktree Setup (for implementation)
+When design is approved and implementation will follow:
+- Announce: "I'm using the Using Git Worktrees skill to set up an isolated workspace."
+- Switch to skills/collaboration/using-git-worktrees
+- Follow that skill's process for directory selection, safety verification, and setup
+- Return here when worktree ready
+
+### Phase 5: Planning Handoff
+Ask: "Ready to create the implementation plan?"
+
+When your human partner confirms (any affirmative response):
+- Announce: "I'm using the Writing Plans skill to create the implementation plan."
+- Switch to skills/collaboration/writing-plans skill
+- Create detailed plan in the worktree
+
+## Remember
+- One question per message during Phase 1
+- Apply YAGNI ruthlessly (reference skills/architecture/reducing-complexity)
+- Explore 2-3 alternatives before settling
+- Present incrementally, validate as you go
+- Announce skill usage at start