Read a paired server's checkout over SSH

Status, checkpoints and the diff of a VPS workspace need its checkout, so the worker now runs entire and git there over SSH. It finds the server's SSH target id with orca environment show and the address in Orca's profile database (sshTargets, opened read-only), refuses addresses that would read as ssh options, and shell-quotes every remote word. BatchMode means the key must be in the Windows ssh-agent; without a target the panel says why. desktopEnv adds ProgramData, without which Windows ssh exits 255 silently.