feat(tui): Task 3.5 — decode + render router.narration as bright narration_llm lines

Add TypeRouterNarration constant, mark it event-bearing, decode golden test,
applyServer case appending RouterEntry{Role:"narration_llm"} with metrics, and
routerRows render branch showing bright ◆ prefix with FgStrong content + metrics suffix.

apps/tui-go/internal/protocol/protocol.go

@@ -44,6 +44,7 @@ const (
 	TypeModelChanged     = "model.changed"
 	TypeModelList        = "model.list"
 	TypeResourceStatus   = "resource.status"
+	TypeRouterNarration  = "router.narration"
 )
 
 // ServerMessage is a flat decode of every server->client variant. Field names
@@ -186,7 +187,8 @@ func (m ServerMessage) IsEventBearing() bool {
 		TypeInferenceStarted, TypeInferenceDone, TypeInferenceTimeout,
 		TypeToolStarted, TypeToolCompleted, TypeToolFailed, TypeToolRejected,
 		TypeToolAssessed,
-		TypeApprovalRequired, TypeApprovalResolved, TypeWorkspaceBound, TypeArtifactCreated:
+		TypeApprovalRequired, TypeApprovalResolved, TypeWorkspaceBound, TypeArtifactCreated,
+		TypeRouterNarration:
 		return true
 	default:
 		return false