fix: show RDG flap badge on 302 and 303 events in SAC UI (0.20.5)

Seaca surfaced flap via Problems; the web UI only flagged 303 in DB and had
no visible label. Resolve flap pairs at read time and show badge plus qwinsta
on both sides of 302→303.

frontend/src/utils/rdgFlap.ts

@@ -0,0 +1,15 @@
+import type { EventSummary } from "../api";
+
+export function hasRdgFlapUi(event: EventSummary): boolean {
+  return Boolean(event.rdg_flap || event.rdg_flap_qwinsta_event_id);
+}
+
+export function rdgFlapQwinstaEventId(event: EventSummary): number | null {
+  if (event.rdg_flap_qwinsta_event_id) return event.rdg_flap_qwinsta_event_id;
+  return event.rdg_flap ? event.id : null;
+}
+
+export function rdgFlapPairLabel(event: EventSummary): string {
+  if (!event.rdg_flap_pair_event_id) return "";
+  return event.type === "rdg.connection.success" ? "→" : "←";
+}