Remove experimental Pi host adapter

[Johnny-xuan]

Summary

• withdraw the experimental Pi host adapter and root Pi package manifest
• remove Pi-only Enter/Return commands, lifecycle integration, tests, CI jobs, and release wiring
• restore Codex-only installation and Project Map guidance
• leave the Codex plugin, persisted TreeWork state model, and project data format unchanged

Verification

• make test
  • 72 Rust tests
  • 64 Project Map tests
  • TypeScript, CLI, hooks, MCP, activation, and macOS quarantine checks
• make validate
• git diff --check

This is intentionally separate from the TreeWork Manual PR.