Add Pi extension package for oh-my-pi integration

[f1shy-dev]

This PR adds Pi (oh-my-pi) integration as a native extension package following the @distracted/opencode pattern.

@distracted/pi package

• Created @distracted/pi package with extension factory pattern
• Maps Pi events (session_start, session_shutdown, agent_start, agent_end, tool_call) to Claude-compatible hooks
• Uses pi- session ID prefix and pi.setLabel("Distracted") for UI
• Zero runtime dependencies; forwards to http://localhost:8765/hook via DISTRACTED_PORT

Server setup integration

• Added packages/server/src/setup/pi.ts with setup/status/remove functions
• Creates ~/.omp/agent/extensions/distracted.mjs re-export for Pi auto-discovery
• Updated AgentType union to include "pi"
• Added "pi" to HookPayload.source type union
• Updated CLI (--setup pi, --remove pi, --status) to support Pi

Other changes

• Updated workspace lockfile after adding new package
• All quality checks (lint, format, knip) pass for both @distracted/pi and @distracted/server

[capy-ai]

LGTM