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/app/server.go

@@ -92,6 +92,12 @@ func (m *Model) applyServer(msg protocol.ServerMessage) {
 	switch msg.Type {
 	case protocol.TypeSessionAnnounced:
 		m.onSessionAnnounced(msg)
+	case protocol.TypeRouterNarration:
+		entry := RouterEntry{Role: "narration_llm", Content: msg.Content}
+		if msg.LatencyMs != nil && msg.TotalTokens != nil {
+			entry.Metrics = &TurnMetrics{LatencyMs: *msg.LatencyMs, TotalTokens: *msg.TotalTokens}
+		}
+		m.appendRouter(msg.SessionID, entry)
 	case protocol.TypeChatTurn:
 		m.routerConnected = true
 		role := "router"