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/lib/nostr/core.ts

@@ -116,10 +116,14 @@ export function addRelay(url: string): void {
 
 export function removeRelay(url: string): void {
   const instance = getNDK();
-  const relay = instance.pool?.relays.get(url);
-  if (relay) {
-    relay.disconnect();
-    instance.pool?.relays.delete(url);
+  // NDK may store URLs with or without trailing slash — check both
+  const variants = [url, url.replace(/\/$/, ""), url.replace(/\/?$/, "/")];
+  for (const v of variants) {
+    const relay = instance.pool?.relays.get(v);
+    if (relay) {
+      relay.disconnect();
+      instance.pool?.relays.delete(v);
+    }
   }
   saveRelayUrls(getStoredRelayUrls().filter((u) => u !== url));
 }