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"

apps/tui-go/internal/app/view.go

@@ -358,6 +358,19 @@ func (m Model) routerRows(w, h int) []string {
 			}
 		case "tool":
 			rows = append(rows, t.span("· tool output ("+itoaLen(e.Content)+" chars) — ^x to view", t.P.Dim))
+		case "narration_llm":
+			diamond := lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Bold(true).Render("◆")
+			lines := wrap(e.Content, w-2)
+			for i, ln := range lines {
+				if i == 0 {
+					rows = append(rows, diamond+" "+t.span(ln, t.P.FgStrong))
+				} else {
+					rows = append(rows, "  "+t.span(ln, t.P.FgStrong))
+				}
+			}
+			if s := metricsSuffix(e.Metrics); s != "" {
+				rows = append(rows, t.span(s, t.P.Faint))
+			}
 		case "narration", "stage":
 			rows = append(rows, t.span(e.Content, t.P.Dim))
 		}