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

internal/beads/beads.go

@@ -603,7 +603,7 @@ func findDatabaseInTree() string {
 // FindAllDatabases scans the directory hierarchy for the closest .beads directory.
 // Returns a slice with at most one DatabaseInfo - the closest database to CWD.
 // Stops searching upward as soon as a .beads directory is found,
-// because in multi-workspace setups (like Gas Town), nested .beads directories
+// because in multi-workspace setups, nested .beads directories
 // are intentional and separate - parent directories are out of scope.
 // Redirect files are supported: if a .beads/redirect file exists, its contents
 // are used as the actual .beads directory path.

internal/beads/beads_multidb_test.go

@@ -64,7 +64,7 @@ func TestFindAllDatabases(t *testing.T) {
 	databases := FindAllDatabases()
 
 	// Should find only the closest database (gt-bzd: stop searching when .beads found)
-	// Parent .beads directories are out of scope in multi-workspace setups like Gas Town
+	// Parent .beads directories are out of scope in multi-workspace setups
 	if len(databases) != 1 {
 		t.Fatalf("expected 1 database (closest only), got %d", len(databases))
 	}