Revert to simple gt-mayor/gt-deacon session names

Reverts the session naming changes from PR #70. Multi-town support
on a single machine is not a real use case - rigs provide project
isolation, and true isolation should use containers/VMs.

Changes:
- MayorSessionName() and DeaconSessionName() no longer take townName parameter
- ParseSessionName() handles simple gt-mayor and gt-deacon formats
- Removed Town field from AgentIdentity and AgentSession structs
- Updated all callers and tests

Generated with Claude Code

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

internal/cmd/agents.go

@@ -35,7 +35,6 @@ type AgentSession struct {
 	Type      AgentType
 	Rig       string // For rig-specific agents
 	AgentName string // e.g., crew name, polecat name
-	Town      string // For mayor/deacon only (town name from session)
 }
 
 // AgentTypeColors maps agent types to tmux color codes.
@@ -136,16 +135,13 @@ func categorizeSession(name string) *AgentSession {
 	session := &AgentSession{Name: name}
 	suffix := strings.TrimPrefix(name, "gt-")
 
-	// Town-level agents: gt-{town}-mayor, gt-{town}-deacon
-	// Check if suffix ends with -mayor or -deacon (new format)
-	if strings.HasSuffix(suffix, "-mayor") {
+	// Town-level agents: gt-mayor, gt-deacon (simple format, one per machine)
+	if suffix == "mayor" {
 		session.Type = AgentMayor
-		session.Town = strings.TrimSuffix(suffix, "-mayor")
 		return session
 	}
-	if strings.HasSuffix(suffix, "-deacon") {
+	if suffix == "deacon" {
 		session.Type = AgentDeacon
-		session.Town = strings.TrimSuffix(suffix, "-deacon")
 		return session
 	}