Add focused Pi host adapter

[Johnny-xuan]

Summary

• add a root Pi package that directly reuses TreeWork's shipped Skill, Rust runtime, transactions, and read-only MCP server
• keep Pi's Agent-tool surface minimal with one lazy loader for Recall, Check, and Project Map
• add explicit /treework-enter and /treework-return host commands for persisted, cwd-bound conversation handoff; prepare the session fork before Enter and recover cancelled switches to paused
• port direct generated-state guardrails and the settled-agent consistency check to Pi lifecycle events
• make Project Map browser behavior host-aware without changing accepted TreeWork state semantics
• document install, use, cache cleanup, rollback, development, and release verification in English and Chinese

The adapter does not add lifecycle states, persisted fields, document types, Team/Runner state, or another source of truth.

Pi session replacement intentionally remains an explicit host command: Pi 0.84.x does not expose session replacement from Agent tool execution, so pretending Enter can be a model tool would either race sibling tools or silently fail. The TreeWork Skill teaches this boundary.

Verification

• make test
  • 72 Rust tests
  • 64 Project Map tests + TypeScript check
  • CLI, read-model, hooks, MCP, activation, quarantine tests
  • Pi guardrail/MCP tests
  • real offline Pi RPC Enter/Return round-trip from a repository subdirectory
  • cancelled Pi switch recovery to paused with no orphan session
• make validate
  • clean Project Map build
  • packaging, plugin, and Skill validation
  • Pi package install/load/remove check
• independent final review: PASS

Closes #6