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

cmd/bd/doctor/maintenance.go

@@ -311,8 +311,8 @@ func CheckCompactionCandidates(path string) DoctorCheck {
 }
 
 // resolveBeadsDir follows a redirect file if present in the beads directory.
-// This handles Gas Town's redirect mechanism where .beads/redirect points to
-// the actual beads directory location.
+// This handles the redirect mechanism where .beads/redirect points to
+// the actual beads directory location (used in multi-clone setups).
 // This is a wrapper around beads.FollowRedirect for use within the doctor package.
 func resolveBeadsDir(beadsDir string) string {
 	return beads.FollowRedirect(beadsDir)