Add the Entire for Orca plugin scaffold and connection check

A trusted-worker Orca plugin with one command, "Entire: Check connection". It finds the focused workspace's path through an Orca terminal handle (or branch and name as a fallback), runs Entire there (through wsl.exe for WSL workspaces), and reports the CLI version, the repo's Entire status and the branch's trail.

Also adds unit tests, a harness that runs the worker inside Orca.exe with a fake host API, CLAUDE.md, the README and docs/PLAN.md.