Instrument gt commands to emit events to activity feed (gt-7aw1m)

Add events.LogFeed calls to the following gt commands:
- nudge.go: Log TypeNudge events when nudging agents
- unsling.go: Log TypeUnhook events when removing work from hooks
- up.go: Log TypeBoot events when starting Gas Town services
- down.go: Log TypeHalt events when stopping Gas Town services
- stop.go: Log TypeKill events when stopping polecat sessions
- polecat_spawn.go: Log TypeSpawn events when spawning polecats

Also add helper functions to events package:
- UnhookPayload: Creates payload for unhook events
- KillPayload: Creates payload for kill events
- HaltPayload: Creates payload for halt events

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/events/events.go

@@ -246,3 +246,26 @@ func EscalationPayload(rig, target, to, reason string) map[string]interface{} {
 		"reason": reason,
 	}
 }
+
+// UnhookPayload creates a payload for unhook events.
+func UnhookPayload(beadID string) map[string]interface{} {
+	return map[string]interface{}{
+		"bead": beadID,
+	}
+}
+
+// KillPayload creates a payload for kill events.
+func KillPayload(rig, target, reason string) map[string]interface{} {
+	return map[string]interface{}{
+		"rig":    rig,
+		"target": target,
+		"reason": reason,
+	}
+}
+
+// HaltPayload creates a payload for halt events.
+func HaltPayload(services []string) map[string]interface{} {
+	return map[string]interface{}{
+		"services": services,
+	}
+}