fix(ui/books): guard null book fields in template; log null titles from PocketBase

ui/src/routes/books/+page.svelte

@@ -58,10 +58,10 @@
 				<!-- Info -->
 				<div class="p-2 flex flex-col gap-1 flex-1">
 					<h2 class="text-xs font-semibold text-zinc-100 line-clamp-2 leading-snug">
-						{book.title}
+						{book.title ?? ''}
 					</h2>
 					{#if book.author}
-						<p class="text-xs text-zinc-400 truncate">{book.author}</p>
+						<p class="text-xs text-zinc-400 truncate">{book.author ?? ''}</p>
 					{/if}
 
 					<div class="mt-auto pt-1 flex items-center justify-between gap-1">