fix(web): 'Unknown Artist' download from artist page + rename itunes*→deezer* identifiers

Fix (the reported bug):
- Deezer's /artist/{id}/albums omits the artist object, so discography album cards had an
  empty artist name → the download modal fell back to the literal "Unknown Artist", which
  poisoned the yt-dlp search ("Unknown Artist <album>") and its artist/channel filter, failing
  with "Nicht eindeutig gefunden".
- deezerLookupArtistAlbums now backfills the known artist name (we're on that artist's page).
- openDlModal now defaults album cards to an ALBUM download (was always Track), so a one-click
  download no longer grabs an album as a single track named after the album.

Rename (requested cleanup, dependency-checked so nothing breaks):
- All frontend itunes* identifiers → deezer* (functions, the ItunesItem-shape field keys
  itunesData/itunesArtistId/itunesFanCount/itunesId, the itunes-album-detail route + DOM ids,
  the badge-itunes CSS class). The backend reads none of these fields, so the boundary is safe.
- Verified: build passes; route/DOM-id/CSS producer↔consumer all consistent; only the factual
  "Apple's iTunes /search 403" comments keep the historical name. SW ns-v62.

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

src/api.js

@@ -271,7 +271,7 @@ export async function romajiConvert(texts) {
 // Apple's iTunes /search returns 403 from server IPs, so Deezer is the metadata backend for
 // everything: search, album/artist lookups AND the "Neu & Beliebt" charts. Free, no key, returns
 // explicit versions + artist images + track durations. Proxied through the backend to avoid any
-// CORS surprises. All results are mapped to the legacy "ItunesItem" shape so the UI + download
+// CORS surprises. All results are mapped to the legacy "DeezerItem" shape so the UI + download
 // flow stay unchanged.
 function _deezerBase() {
   return S.cfg.backendUrl ? `${S.cfg.backendUrl}/api/deezer` : 'https://api.deezer.com';
@@ -306,23 +306,23 @@ function _dzArtist(a) {
     artistId: a.id, artistName: a.name,
     artworkUrl100: a.picture_big || a.picture_medium || '',
     // Deezer's artist search does NOT rank by popularity — several artists can share a name
-    // (5× "Joji"). fanCount lets us pick the one the user means (see itunesSearch + detail.js).
+    // (5× "Joji"). fanCount lets us pick the one the user means (see deezerSearch + detail.js).
     fanCount: a.nb_fan ?? undefined,
   };
 }
 
 // Last search outcome: null = ok, else HTTP status or 'network'. Read by the search view to tell
 // "no results" apart from "search backend down".
-let _itunesLastError = null;
-export function itunesLastError() { return _itunesLastError; }
+let _deezerLastError = null;
+export function deezerLastError() { return _deezerLastError; }
 
 // Keeps the old name so all callers stay unchanged. entity: musicTrack | album | musicArtist.
-export async function itunesSearch(query, entity='musicTrack', limit=25) {
+export async function deezerSearch(query, entity='musicTrack', limit=25) {
   try {
     const path = entity === 'album' ? 'search/album' : entity === 'musicArtist' ? 'search/artist' : 'search';
     const r = await fetch(`${_deezerBase()}/${path}?q=${encodeURIComponent(query)}&limit=${limit}`);
-    if (!r.ok) { _itunesLastError = r.status; return []; }
-    _itunesLastError = null;
+    if (!r.ok) { _deezerLastError = r.status; return []; }
+    _deezerLastError = null;
     const txt = await r.text();
     const data = (txt ? JSON.parse(txt) : {}).data || [];
     if (entity === 'album')      return data.map(_dzAlbum);
@@ -330,12 +330,12 @@ export async function itunesSearch(query, entity='musicTrack', limit=25) {
     // (Deezer returns them in an unhelpful order — the real "Joji" isn't first).
     if (entity === 'musicArtist') return data.map(_dzArtist).sort((x, y) => (y.fanCount || 0) - (x.fanCount || 0));
     return data.map(_dzTrack);
-  } catch { _itunesLastError = 'network'; return []; }
+  } catch { _deezerLastError = 'network'; return []; }
 }
 
 // Album tracks (for the album detail view + album download). Deezer's /album/{id} embeds tracks +
 // album-level release/genre/cover, so one request gives everything.
-export async function itunesLookupAlbum(collectionId) {
+export async function deezerLookupAlbum(collectionId) {
   try {
     const r = await fetch(`${_deezerBase()}/album/${collectionId}`);
     const a = await r.json();
@@ -351,17 +351,23 @@ export async function itunesLookupAlbum(collectionId) {
   } catch { return []; }
 }
 
-export async function itunesLookupArtistSongs(artistId, limit=15) {
+export async function deezerLookupArtistSongs(artistId, limit=15) {
   try {
     const r = await fetch(`${_deezerBase()}/artist/${artistId}/top?limit=${limit}`);
     return ((await r.json()).data || []).map(_dzTrack);
   } catch { return []; }
 }
 
-export async function itunesLookupArtistAlbums(artistId, limit=100) {
+// Deezer's /artist/{id}/albums list OMITS the artist object, so _dzAlbum yields artistName:''.
+// We already know whose page this is → backfill artistName so downstream download/detail cards
+// don't fall back to the literal "Unknown Artist" (which poisoned the yt-dlp search).
+export async function deezerLookupArtistAlbums(artistId, limit=100, artistName='') {
   try {
     const r = await fetch(`${_deezerBase()}/artist/${artistId}/albums?limit=${limit}`);
-    return ((await r.json()).data || []).map(_dzAlbum).filter(a => a.collectionType === 'Album');
+    return ((await r.json()).data || [])
+      .map(_dzAlbum)
+      .filter(a => a.collectionType === 'Album')
+      .map(a => (a.artistName ? a : { ...a, artistName }));
   } catch { return []; }
 }
 
@@ -375,7 +381,7 @@ export async function deezerArtistImage(artistId) {
 
 // "Neu & Beliebt" — Deezer's global chart (Apple's charts RSS needed a proxy and the search
 // fallback is 403 from server IPs). Mapped to { name, artistName, artworkUrl, artworkUrl100 }.
-export async function itunesTopCharts() {
+export async function deezerTopCharts() {
   try {
     const r = await fetch(`${_deezerBase()}/chart/0/albums?limit=50`);
     const d = await r.json();
@@ -386,7 +392,7 @@ export async function itunesTopCharts() {
   } catch { return []; }
 }
 
-export async function itunesTopSongs() {
+export async function deezerTopSongs() {
   try {
     const r = await fetch(`${_deezerBase()}/chart/0/tracks?limit=50`);
     const d = await r.json();