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/main.go

@@ -147,8 +147,8 @@ var rootCmd = &cobra.Command{
 		// Set up signal-aware context for graceful cancellation
 		rootCtx, rootCancel = signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 
-		// Signal Gas Town daemon about bd activity (best-effort, for exponential backoff)
-		defer signalGasTownActivity()
+		// Signal orchestrator daemon about bd activity (best-effort, for exponential backoff)
+		defer signalOrchestratorActivity()
 
 		// Apply verbosity flags early (before any output)
 		debug.SetVerbose(verboseFlag)