Add a focused Pi host adapter

[Johnny-xuan]

Problem

TreeWork's transaction runtime and project-state model are host-neutral, but the shipped package currently assumes Codex for skill discovery, hooks, MCP registration, and branch-worktree handoff. Pi can load Agent Skills and extensions, but it needs a focused adapter that preserves TreeWork's existing document, transaction, lifecycle, isolation, and verification semantics.

Proposed scope

Add an MIT-licensed Pi package adapter that:

• loads the existing TreeWork skill without duplicating its source;
• exposes the existing read-only TreeWork MCP server through Pi's lazy MCP adapter configuration;
• ports generated-state guardrails to Pi extension tool hooks;
• runs the existing stop/check boundary when a Pi agent settles;
• supports TreeWork branch worktree handoff by moving the Pi conversation into a session whose cwd is the entered worktree, while preserving conversation history;
• documents installation and verification without copying credentials or proprietary host implementation.

The adapter must not add TreeWork lifecycle states, persisted fields, document types, Team/Runner state, or a second source of truth.

Acceptance

• Pi package loads on the supported Pi version with a minimal always-active surface.
• Existing tw runtime and MCP checks remain authoritative.
• Guardrail and workspace-switch behavior have automated tests.
• make test and make validate pass.
• Installation and rollback are documented.