The refinery start command was only updating state.json without
actually starting a session. Now it spawns a tmux session named
gt-{rig}-refinery that runs the refinery in foreground mode.
Also updated Stop() and Status() to properly check tmux session
state alongside the PID-based tracking for backwards compatibility.
Fixes: gt-17zr
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>