feat(artist): pin a local artist to a specific Deezer artist (same-name fix, shared)

Fixes same-name collisions where NovaSonic guessed the wrong Deezer artist (e.g.
'Nana' → a random DJ): fans, top songs, missing albums and the hero image were all
off. A '⚙ Falscher Künstler?' button on the artist page opens a picker (same-name
Deezer candidates with image + fan count); the chosen mapping is stored SERVER-SIDE
(shared across users, like the romaji overrides) in /data/deezer-artist-overrides.json.

Once pinned, the artist page short-circuits the name search to the pinned Deezer id
(drives albums/top-songs/fans) and overrides the hero image with the pinned artist's
Deezer picture (NovaSonic-side, so it works even for tag-merged same-name artists —
Navidrome can't disambiguate them without an MBID). New endpoints
GET/POST/DELETE /api/artist-overrides; api.js load/get/set/remove; loaded at startup.
SW cache -> ns-v74. Needs on-device runtime test.

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

src/main.js

@@ -1,9 +1,10 @@
 import { S } from './state.js';
 import { toast } from './utils.js';
-import { api, fetchRomajiIndex, loadRomajiOverrides } from './api.js';
+import { api, fetchRomajiIndex, loadRomajiOverrides, loadArtistOverrides } from './api.js';
 import { injectPWA } from './pwa.js';
 import { initPlayLog } from './player/scrobbleLog.js';
 import { openStats, closeStats } from './ui/stats.js';
+import { closeArtistPin, clearArtistPin } from './ui/artistPin.js';
 import { loadSavedTheme } from './themes.js';
 import { initScrollRows } from './ui/components.js';
 import {
@@ -111,6 +112,7 @@ async function startApp() {
   }
   initNotifBell();
   initPlayLog();   // flush any queued plays to the scrobble service (offline-safe)
+  loadArtistOverrides().catch(() => {});   // pinned same-name artist → Deezer mappings (shared)
   // Wait for overrides before restoring player bar so disp* functions have the cache ready
   loadRomajiOverrides().catch(() => {}).then(() => { _restoreLastPlayed(); });
   if(localStorage.getItem('ns_radio')==='1') { S.radioMode=true; _applyRadioBtn(); }
@@ -334,6 +336,7 @@ Object.assign(window, {
   openSettings, closeSettings, saveSettings, confirmDisconnect, checkBackend,
   openSidebar, closeSidebar, switchNavMode, showCtxMenu,
   openStats, closeStats,
+  closeArtistPin, clearArtistPin,
   // Views
   loadAlbums, loadStarred, loadRandom, filterStarred, filterPlaylist,
   plReorderEnter, plReorderSave, plReorderCancel, toggleAllGenres,