fix(web): Deezer artist images + rename the search label

- Search artist cards now use the Deezer artist picture directly (Deezer artists carry
  a photo, unlike iTunes entities) instead of a null image + an extra album lookup;
  the lookup stays only as a fallback when no picture is present.
- Non-local (Deezer) artist pages: fetch the Deezer artist picture (/artist/{id}) for
  the hero photo, which was blank because getArtistImage only runs for Navidrome artists.
- Label "iTunes Künstler" → "Deezer Künstler".

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/api.js

@@ -372,6 +372,14 @@ export async function itunesLookupArtistAlbums(artistId, limit=100) {
   } catch { return []; }
 }
 
+// Deezer artist photo (for the hero on non-local artist pages). iTunes artist entities had none.
+export async function deezerArtistImage(artistId) {
+  try {
+    const a = await (await fetch(`${_deezerBase()}/artist/${artistId}`)).json();
+    return a.picture_xl || a.picture_big || a.picture_medium || null;
+  } catch { return null; }
+}
+
 export async function itunesTopCharts() {
   const urls = [_chartsUrl('de', 'albums'), _chartsUrl('us', 'albums')];
   for(const url of urls) {