fix(web): restore album-page back link; loosen test matchers

The initial Task 13 pass dropped the back-chevron link above the hero
to satisfy a strict getByRole('link', {name: /Miles Davis/}) matcher
that was finding both the back link and the inline hero-artist link.

Better fix: keep the back affordance users expect, and use matchers
that accept ambiguity — getAllByRole for the hero check, and a
strict '^← …' regex for the back-link assertion.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/src/routes/albums/[id]/+page.svelte

@@ -35,6 +35,13 @@
     <LibrarySkeleton variant="album" />
   {:else if query.data}
     {@const album = query.data}
+    <a
+      href={`/artists/${album.artist_id}`}
+      class="text-sm text-text-secondary hover:text-text-primary"
+    >
+      ← {album.artist_name}
+    </a>
+
     <header class="flex flex-col gap-4 md:flex-row md:items-end">
       <img
         src={album.cover_url}