feat: add relay status indicator for local-only/offline mode

- Create RelayStatusIndicator component with plane icon for local-only mode
- Position indicator in bottom-left corner with amber styling
- Show when only local relays are connected or completely offline
- Hide indicator when remote relays are available (normal operation)
- Add pulsing globe icon animation to indicate checking for connection
- Include hover effects and smooth transitions
- Auto-adjust position when sidebar is collapsed
- Display relay count and clear status messages

src/components/ThreePaneLayout.tsx

@@ -6,6 +6,7 @@ import { HighlightsPanel } from './HighlightsPanel'
 import Settings from './Settings'
 import Toast from './Toast'
 import { HighlightButton } from './HighlightButton'
+import { RelayStatusIndicator } from './RelayStatusIndicator'
 import { ViewMode } from './Bookmarks'
 import { Bookmark } from '../types/bookmarks'
 import { Highlight } from '../types/highlights'
@@ -149,6 +150,7 @@ const ThreePaneLayout: React.FC<ThreePaneLayoutProps> = (props) => {
           highlightColor={props.settings.highlightColor || '#ffff00'}
         />
       )}
+      <RelayStatusIndicator relayPool={props.relayPool} />
       {props.toastMessage && (
         <Toast
           message={props.toastMessage}