feat: Deezer artist photo fallback for local artists with no Navidrome image

Niche local artists (e.g. N!GHT) whose Navidrome metadata agents have no image showed a
blank hero. Now, when Navidrome has no artist image, the hero falls back to the matched
Deezer artist's photo (Navidrome image → Deezer photo → album cover), on web + Android.

- Web (detail.js): the Deezer-photo fallback previously ran only for non-local artists;
  now it runs whenever the Navidrome image is absent, local or not.
- Android: ArtistViewModel captures the matched Deezer artist's photo (deezerImage);
  ArtistDetailScreen uses it as the hero fallback.
SW ns-v56.

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

src/views/detail.js

@@ -178,16 +178,21 @@ export async function loadArtistDetail(artist) {
   const itunesArtistId = knownItunes ?? iArtistMatch?.artistId ?? null;
   if (!knownFans) _showFans(iArtistMatch?.fanCount); // local artist: show the matched Deezer artist's fans
 
-  // Non-local (Deezer) artist has no Navidrome photo — fetch the Deezer artist picture for the hero.
-  if (!hasND && itunesArtistId && pfpWrap) {
-    const dzImg = iArtistMatch?.artworkUrl100 || await deezerArtistImage(itunesArtistId);
-    if (dzImg) {
-      const pfpImg = document.createElement('img');
-      pfpImg.className = 'artist-hero-pfp';
-      pfpImg.onload = pfpImg.onerror = () => { if (bgEl) bgEl.style.backgroundImage = `url('${dzImg}')`; _revealHero(); };
-      pfpImg.src = dzImg;
-      pfpWrap.prepend(pfpImg);
-      document.getElementById('artist-hero-pfp-initial')?.style.setProperty('display', 'none');
+  // Artist photo: Navidrome (from its metadata agents) first; if it has none, fall back to the
+  // matched Deezer artist's picture. Covers non-local Deezer artists AND niche local artists
+  // (e.g. N!GHT) that Navidrome's agents have no art for — the hero was blank for those before.
+  if (itunesArtistId && pfpWrap) {
+    const ndImg = await imgP.catch(() => null);
+    if (!ndImg) {
+      const dzImg = iArtistMatch?.artworkUrl100 || await deezerArtistImage(itunesArtistId);
+      if (dzImg) {
+        const pfpImg = document.createElement('img');
+        pfpImg.className = 'artist-hero-pfp';
+        pfpImg.onload = pfpImg.onerror = () => { if (bgEl) bgEl.style.backgroundImage = `url('${dzImg}')`; _revealHero(); };
+        pfpImg.src = dzImg;
+        pfpWrap.prepend(pfpImg);
+        document.getElementById('artist-hero-pfp-initial')?.style.setProperty('display', 'none');
+      }
     }
   }