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/App.tsx

@@ -20,6 +20,7 @@ import { BookmarkView } from "./components/bookmark/BookmarkView";
 import { HashtagFeed } from "./components/feed/HashtagFeed";
 import { PodcastsView } from "./components/podcast/PodcastsView";
 import { PodcastPlayerBar } from "./components/podcast/PodcastPlayerBar";
+import { ToastContainer } from "./components/shared/ToastContainer";
 import { HelpModal } from "./components/shared/HelpModal";
 import { useUIStore } from "./stores/ui";
 import { useUpdater } from "./hooks/useUpdater";
@@ -108,6 +109,7 @@ function App() {
       </main>
       </div>
       <PodcastPlayerBar />
+      <ToastContainer />
       {showHelp && <HelpModal onClose={toggleHelp} />}
     </div>
   );