Add relay status badge, toast notifications, per-tab feed timestamps, relay UX improvements

- Relay status badge in feed header: shows connected/total relay count with
  color coding (green >75%, yellow 25-75%, red <25%), hover tooltip with
  per-relay status
- Toast notification system: transient messages for connection lost,
  reconnecting, relay reset, and back-online events
- Per-tab "last updated" relative timestamp in feed header (global,
  following, trending tracked independently)
- Consolidated all relay management into RelaysView (removed duplicate
  relay section from Settings); per-relay remove button on health cards
- Show all supported NIP badges on relay cards (was filtering to 11 notable)
- Tooltips on relay status dots explaining green/yellow/red/gray meaning
- Fix relay removal with trailing-slash URL normalization
- Fix stale health results lingering after relay removal
- Add acknowledgements section to README

src/hooks/useRelayStatus.ts

@@ -0,0 +1,37 @@
+import { useState, useEffect } from "react";
+import { getNDK } from "../lib/nostr";
+
+interface RelayInfo {
+  url: string;
+  connected: boolean;
+}
+
+interface RelayStatus {
+  connectedCount: number;
+  totalCount: number;
+  relays: RelayInfo[];
+}
+
+function readPool(): RelayStatus {
+  const ndk = getNDK();
+  const relays = Array.from(ndk.pool?.relays?.values() ?? []).map((r) => ({
+    url: r.url,
+    connected: r.connected,
+  }));
+  return {
+    connectedCount: relays.filter((r) => r.connected).length,
+    totalCount: relays.length,
+    relays,
+  };
+}
+
+export function useRelayStatus(): RelayStatus {
+  const [status, setStatus] = useState<RelayStatus>(readPool);
+
+  useEffect(() => {
+    const id = setInterval(() => setStatus(readPool()), 5000);
+    return () => clearInterval(id);
+  }, []);
+
+  return status;
+}