style(frontend): show pulsating zero when loading total balance (#2086)

# Motivation

While it loads the total balance, a pulsating zero will be showed
(similar to what happens to the single token pages).


https://github.com/user-attachments/assets/83eb0a6e-ee2a-4ed1-b25d-09508dd2ccb3

src/frontend/src/lib/components/exchange/ExchangeBalance.svelte

@@ -17,7 +17,7 @@
 		{#if $exchangeInitialized}
 			{formatUSD(totalUsd)}
 		{:else}
-			​
+			<span class="animate-pulse">{formatUSD(0)}</span>
 		{/if}
 	</output>
 </span>