Remove state files from witness and refinery managers, following
the "Discover, Don't Track" principle. Tmux session existence is
now the source of truth for running state (like deacon).
Changes:
- Add IsRunning() that checks tmux HasSession
- Change Status() to return *tmux.SessionInfo
- Remove loadState/saveState/stateManager
- Simplify Start()/Stop() to not use state files
- Update CLI commands (witness/refinery/rig) for new API
- Update tests to be ZFC-compliant
This fixes state file divergence issues where witness/refinery
could show "running" when the actual tmux session was dead.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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