refactor: remove Gas Town references from codebase

Replace Gas Town-specific terminology with generic orchestrator concepts:
- "Gas Town" → "orchestrator" or "multi-clone"
- Hardcoded ~/gt/ paths → GT_ROOT environment variable
- signalGasTownActivity → signalOrchestratorActivity
- GUPP → hook-based work assignment

Updated 21 files across CHANGELOG, cmd/bd/, internal/, docs/, scripts.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Executed-By: beads/crew/dave
Rig: beads
Role: crew

scripts/bump-version.sh

@@ -29,16 +29,14 @@ set -e
 #   For guided, resumable releases with multiple agents:
 #   bd template instantiate bd-6s61 --var version=X.Y.Z --assignee <identity>
 #
-# IMPORTANT: In Gas Town, run from mayor/rig to avoid git conflicts with bd sync
+# IMPORTANT: In multi-clone setups, run from the main clone to avoid git conflicts
 # =============================================================================
 #
-# Gas Town agents share a beads database at mayor/rig/.beads/. The bd sync
+# Multi-clone setups share a beads database at a central location. The bd sync
 # command commits from that clone. Running version bumps from a different
-# clone (e.g., crew/dave) causes push conflicts when bd sync tries to push.
+# clone causes push conflicts when bd sync tries to push.
 #
-# Always run releases from the rig root:
-#
-#   cd ~/gt/beads/mayor/rig && ./scripts/bump-version.sh X.Y.Z --commit --tag --push --all
+# Always run releases from the main clone (the one that owns the beads database).
 #
 # =============================================================================