Replace tmux session scanning with proper rig discovery: - Primary: Load rigs from mayor/rigs.json via rig manager - Fallback: Scan town directory for .beads or config.json - Handle rigs without running witnesses gracefully Closes gt-oc2 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>