Update theme configuration to 'system' and streamline relay URLs in App component

src/App.tsx

@@ -32,12 +32,10 @@ const queryClient = new QueryClient({
 });
 
 const defaultConfig: AppConfig = {
-  theme: "light",
+  theme: "system",
   relayMetadata: {
     relays: [
-      { url: 'wss://relay.ditto.pub', read: true, write: true },
-      { url: 'wss://relay.nostr.band', read: true, write: true },
-      { url: 'wss://relay.damus.io', read: true, write: true },
+      { url: 'wss://relay.layer.systems', read: true, write: true },
     ],
     updatedAt: 0,
   },