feat(ui): hover zoom on viewer thumbnail strip

- Thumbnails scale their image on pointer hover and keyboard focus
- Tile size and strip layout stay unchanged

frontend/src/lib/components/Viewer.svelte

@@ -443,7 +443,7 @@
 		{#each photos as photo, i (photo.id)}
 			<button
 				type="button"
-				class="h-16 w-16 shrink-0 overflow-hidden rounded border {i === index
+				class="group h-16 w-16 shrink-0 overflow-hidden rounded border {i === index
 					? 'border-primary'
 					: 'border-border'}"
 				onclick={() => onIndexChange(i)}
@@ -454,7 +454,7 @@
 					<img
 						src={photo.thumb_url}
 						alt=""
-						class="h-full w-full object-cover"
+						class="h-full w-full object-cover transition-transform duration-200 group-hover:scale-105 group-focus-visible:scale-105"
 						loading="lazy"
 					/>
 				{:else}