feat(tui): truthful-state §2 — last-event clock + unknown-event raw fallback

Implements the load-bearing TUI-requirements §2 hard requirements:

- Last-event clock: "last event Ns ago" always visible in the status bar while
  in-session, updating every frame tick. Turns warn-colored when an active session
  has gone quiet past the stale threshold — the "thinking vs hung" tell. The
  WebSocket connection indicator (●/◌/○) already covers immediate drop visibility.
- Unknown-event raw fallback: applyServer now surfaces any unrecognized,
  session-scoped event type as a raw row in the event stream instead of silently
  dropping it (the frontend must not lie by omission). Recognized-but-unrendered
  types (router.response, protocol_error) get an explicit no-op so the default
  branch means genuinely unknown.

Tests: agoLabel formatting, unknown-event surfaces-as-row, known-ignored
no-spurious-row. Preview "session" frame exercises the clock.

Deferred: the full Go↔Kotlin per-event-type render matrix (§2 last bullet) — a
larger fixture effort than the core behaviors landed here.

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

@@ -322,6 +322,22 @@ func (m *Model) applyServer(msg protocol.ServerMessage) {
 		if m.configIndex >= len(m.configFields) {
 			m.configIndex = 0
 		}
+	case protocol.TypeRouterResponse, protocol.TypeProtocolError:
+		// Recognized but intentionally not rendered here: router.response is
+		// superseded by chat.turn events on the global stream, and protocol_error is
+		// a transport diagnostic. Explicit no-op so the default below means *unknown*.
+	default:
+		// Unknown-event raw fallback (TUI-requirements §2): a session-scoped event
+		// type this client doesn't recognize is surfaced as a raw row in the event
+		// stream, never silently dropped — the frontend must not lie by omission.
+		if msg.SessionID != "" {
+			s := m.ensureSession(msg.SessionID)
+			at := msg.OccurredAt
+			if at == 0 {
+				at = nowMillis()
+			}
+			s.addEvent(at, msg.Type, "(raw — unrendered event)")
+		}
 	}
 
 	// Background-update badge for non-selected sessions.