feat: disambiguate same-name artists by Deezer fan count + show fans

Deezer's artist search doesn't rank by popularity, so a name collision (5 artists named
"Joji") returned a niche one first (62 fans) instead of the real Joji (559k) — the artist
page then loaded the wrong discography and owned songs didn't show as downloaded.

- api.js: _dzArtist carries fanCount (nb_fan); artist search sorts by fanCount desc.
- search.js: artist cards show the fan count as subtitle; fan count passed to the artist page.
- detail.js: pick the most-popular name match (not the first); for local Navidrome artists
  with a real collision (>=2 same-name candidates), tie-break by SONG OVERLAP — prefer the
  Deezer candidate whose top tracks actually overlap the library (each artist has different
  songs, so this nails the right person). Costs a few calls only on a collision.
- Artist hero shows "<n> Fans" (immediately for global-search artists, after match for local).
- Android: DzArtist.nb_fan + /search/artist sorted by nb_fan so the right artist is first.
- Also: web global-search "unavailable" message now says Deezer, not Apple. SW ns-v52.

Verified live against Deezer: both fan-sort and overlap select the real Joji (id 5078097).

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

android/app/src/main/kotlin/com/novasonic/app/api/ItunesClient.kt

@@ -49,7 +49,9 @@ object ItunesClient {
             val tracksD  = async { runCatching { http.get("$BASE/search")        { parameter("q", query); parameter("limit", limit) }.body<DzList<DzTrack>>().data }.getOrDefault(emptyList()) }
             val albumsD  = async { runCatching { http.get("$BASE/search/album")  { parameter("q", query); parameter("limit", 12)    }.body<DzList<DzAlbum>>().data }.getOrDefault(emptyList()) }
             val artistsD = async { runCatching { http.get("$BASE/search/artist") { parameter("q", query); parameter("limit", 8)     }.body<DzList<DzArtist>>().data }.getOrDefault(emptyList()) }
-            val results = artistsD.await().map { it.toItunesItem() } +
+            // Deezer doesn't rank artists by popularity — sort by nb_fan so a name collision
+            // (5× "Joji") resolves to the artist the user means (real Joji has 559k fans, not 62).
+            val results = artistsD.await().sortedByDescending { it.nb_fan ?: 0 }.map { it.toItunesItem() } +
                 albumsD.await().map { it.toItunesItem() } +
                 tracksD.await().map { it.toItunesItem() }
             ItunesSearchResponse(results = results)

android/app/src/main/kotlin/com/novasonic/app/api/model/DeezerModels.kt

@@ -18,6 +18,7 @@ data class DzArtist(
     val picture_medium: String? = null,
     val picture_big: String? = null,
     val picture_xl: String? = null,
+    val nb_fan: Long? = null,   // popularity — disambiguates same-name artists (5× "Joji")
 )
 
 @Serializable