feat(icons): centralize agent icons and add to all displays

- Mayor: 🎩 (top hat)
- Deacon: 🦉 (owl)
- Witness: 👁 (eye)
- Refinery: 🏭 (factory)
- Crew: 🧑‍💻 (technologist)
- Polecat: 😺 (happy cat)

Icons now show in:
- tmux status lines for all agent types
- gt status rig indicators
- gt witness status output
- gt agents popup menu

internal/cmd/agents.go

@@ -44,10 +44,10 @@ var AgentTypeColors = map[AgentType]string{
 // AgentTypeIcons maps agent types to display icons.
 var AgentTypeIcons = map[AgentType]string{
 	AgentMayor:    "🎩",
-	AgentDeacon:   "🗼",
+	AgentDeacon:   "🦉",
 	AgentWitness:  "👁",
 	AgentRefinery: "🏭",
-	AgentCrew:     "👷",
+	AgentCrew:     "🧑‍💻",
 	AgentPolecat:  "😺",
 }