feat(font-list): show empty state when search yields no fonts

Adds an `empty` snippet prop to FontVirtualList and supplies it from the
sidebar FontList. Settled queries with zero results now render a centered
"No typefaces found" label instead of a blank list area.

src/widgets/ComparisonView/ui/FontList/FontList.svelte

@@ -104,6 +104,12 @@ function isFontReady(font: UnifiedFont): boolean {
             gap={2}
             class="bg-transparent min-h-0 h-full scroll-stable py-2 pl-6 pr-4"
         >
+            {#snippet empty()}
+                <div class="px-6 py-12 flex items-center justify-center">
+                    <Label variant="muted" size="sm">No typefaces found</Label>
+                </div>
+            {/snippet}
+
             {#snippet skeleton()}
                 <div class="py-2.5 md:py-3 px-7">
                     {#each { length: 50 } as _, index (index)}