feat(skills): add Pi Coding Agent support

[DaviRain-Su]

Summary

Add new skill for Pi Coding Agent CLI integration, expanding the autonomous AI agents ecosystem.

What's Added

New skill pi in skills/autonomous-ai-agents/pi/SKILL.md providing:

• One-shot task execution: pi "Implement feature X"
• Interactive TUI sessions: Background mode with progress monitoring
• PR review workflow: Safe review in temp directories
• Parallel work patterns: Multiple Pi instances with worktrees

About Pi

Pi is an open-source AI coding agent from the pi-mono monorepo by @badlogic:

• Interactive coding agent with TUI and CLI modes
• Provider-agnostic (OpenAI, Anthropic, etc.)
• MIT licensed

Installation

npm install -g @mariozechner/pi-coding-agent

Usage

# One-shot task
terminal(command="pi 'Add error handling'", workdir="~/project")

# Background session
terminal(command="pi", workdir="~/project", background=true, pty=true)

Testing

• Skill file follows existing format (codex, opencode, claude-code)
• YAML frontmatter is valid
• Examples use correct terminal/process tool syntax

Related

Closes #3228