Copilot CLI 1.0.79-3 added /worktree new (start a session in a new
worktree). Hermes already has hermes -w launch-time isolation; this adds
the mid-session counterpart: /worktree new [name] creates a tree under
.worktrees/ (remote-tip base, worktree_sync honored), retargets
TERMINAL_CWD + process cwd, and registers the same keep-if-unpushed exit
cleanup. /worktree shows the active tree; /worktree list lists them.
Named trees skip the hermes- prefix so the startup pruner ages them on
the slower named-tree schedule.
