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/golden_test.go

@@ -99,6 +99,17 @@ func TestDecodeGoldenServerFrames(t *testing.T) {
 				}
 			},
 		},
+		{
+			name:      "router.narration carries content + metrics",
+			json:      `{"type":"router.narration","sessionId":"s1","content":"moving on","stageId":"validate","latencyMs":2000,"totalTokens":120,"sequence":10,"sessionSequence":5}`,
+			wantType:  TypeRouterNarration,
+			eventBear: true,
+			check: func(t *testing.T, m ServerMessage) {
+				if m.Content != "moving on" || m.LatencyMs == nil || *m.LatencyMs != 2000 || m.TotalTokens == nil || *m.TotalTokens != 120 {
+					t.Fatalf("router.narration: %+v", m)
+				}
+			},
+		},
 		{
 			name:      "snapshot_complete (non-event control frame)",
 			json:      `{"type":"snapshot_complete"}`,