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/components/feed/RelayStatusBadge.tsx

@@ -0,0 +1,57 @@
+import { useState } from "react";
+import { useRelayStatus } from "../../hooks/useRelayStatus";
+
+function shortenUrl(url: string): string {
+  return url.replace(/^wss?:\/\//, "").replace(/\/$/, "");
+}
+
+export function RelayStatusBadge() {
+  const { connectedCount, totalCount, relays } = useRelayStatus();
+  const [hovered, setHovered] = useState(false);
+
+  const ratio = totalCount > 0 ? connectedCount / totalCount : 0;
+  const colorClass =
+    ratio > 0.75
+      ? "text-success"
+      : ratio > 0.25
+        ? "text-warning"
+        : "text-danger";
+  const dotClass =
+    ratio > 0.75
+      ? "bg-success"
+      : ratio > 0.25
+        ? "bg-warning"
+        : "bg-danger";
+
+  if (totalCount === 0) return null;
+
+  return (
+    <span
+      className={`relative ${colorClass} text-[11px] flex items-center gap-1 cursor-default`}
+      onMouseEnter={() => setHovered(true)}
+      onMouseLeave={() => setHovered(false)}
+    >
+      <span className={`w-1.5 h-1.5 rounded-full ${dotClass} inline-block`} />
+      {connectedCount}/{totalCount} relays
+
+      {hovered && (
+        <div className="absolute right-0 top-full mt-1 bg-bg-raised border border-border p-2 z-50 min-w-[200px] shadow-lg">
+          {relays
+            .sort((a, b) => (a.connected === b.connected ? 0 : a.connected ? -1 : 1))
+            .map((r) => (
+              <div key={r.url} className="flex items-center gap-2 py-0.5">
+                <span
+                  className={`w-1.5 h-1.5 rounded-full shrink-0 ${
+                    r.connected ? "bg-success" : "bg-danger"
+                  }`}
+                />
+                <span className="text-[11px] text-text-dim truncate">
+                  {shortenUrl(r.url)}
+                </span>
+              </div>
+            ))}
+        </div>
+      )}
+    </span>
+  );
+}