refactor(#59): Verify that 'transactions' is always defined before iteration

src/routes/account/+page.svelte

@@ -106,6 +106,7 @@
 			<section class="space-y-4">
 				<h2 class="text-xl font-semibold">Billing History</h2>
 				<ul class="space-y-3">
+					{#if transactions}
 						{#each transactions as transaction}
 							<li class="flex justify-between p-4 border border-gray-200 rounded-md">
 								<div>
@@ -124,6 +125,7 @@
 								{/if}
 							</li>
 						{/each}
+					{/if}
 				</ul>
 			</section>
 		</div>