Default remote_path to <checkout_name>/<stage_name>

For stages added in workspace mode (forest add), the default remote layout is <checkout_name>/<stage_name>, not the bare stage name. Checkouts commonly share one physical remote root (here, warm = /Volumes/trials); a bare default makes two trials' identically-named stages (e.g. sequencing) map to the same remote path and overwrite each other. Prefixing by the unique checkout name isolates trials and matches the existing G003/sorting convention.

Consequences

• forest add writes remote_path: <checkout_name>/<stage_name> for new stages.
• Adopted legacy stages keep their explicit remote_path.
• Name checkouts after the trial so added and adopted stages share one remote prefix.