feat(web): scale ArtistCard fallback Disc3 to fill the circle

The Disc3 fallback was rendered at fixed 32px regardless of card size,
so on a 144px (or larger) circular ArtistCard it floated in mostly-empty
space. Now sized via h-4/5 w-4/5 so it tracks the parent — ~80%
fill, much more recognisable as a record/disc. Stroke-width drops from
1.5 to 1 so the heavier line work doesn't overwhelm at the larger size.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/lib/components/ArtistCard.svelte

@@ -39,7 +39,7 @@
         />
       {:else}
         <div class="flex h-full w-full items-center justify-center">
-          <Disc3 size={32} strokeWidth={1.5} class="text-text-muted" />
+          <Disc3 strokeWidth={1} class="h-4/5 w-4/5 text-text-muted" />
         </div>
       {/if}
       <button