sessionWorkDir had cases for mayor, deacon, crew, witness, and refinery
but not polecats. When gt handoff was run from a polecat session like
gt-tanwa_info-slit, it failed with "unknown session type".
Fix uses session.ParseSessionName to parse the session name and extract
rig/name for polecat sessions, mapping to <townRoot>/<rig>/polecats/<name>.
Fixes: gm-lie6
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
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