feat(discord): add server cover art source (#462)

* feat(discord): add server cover art source

The old Apple Music toggle is replaced with a radio selector which let's you choose
between Apple Music, Server and no image.

It's important to note that the server needs to be publicly accessible.

Translations have been added for all locales

* feat(discord): toggle UI for cover source and tightened defaults

- Replace cover-source radio buttons with three indented sub-toggles
  (none / server / apple) under Discord Rich Presence; mutex via
  setDiscordCoverSource — turning one on flips the others off.
- Default discordCoverSource is now 'server' for fresh installs
  (opt-in friendly: own server, no third-party data leak). Existing
  users keep their state via the legacy bool migration.
- Tighten template defaults: details {artist}, state {title}, largeText
  unchanged. Existing users keep their persisted values.

* docs(contributors): credit Sayykii + changelog entry for #462

---------

Co-authored-by: Psychotoxical <171614930+Psychotoxical@users.noreply.github.com>

src/locales/de.ts

@@ -709,8 +709,11 @@ export const deTranslation = {
     useCustomTitlebarDesc: 'Ersetzt die System-Titelleiste durch eine eingebaute, die zum App-Theme passt. Deaktivieren, um die native GNOME/GTK-Titelleiste zu verwenden.',
     linuxWebkitSmoothScroll: 'Sanftes Mausrad (Linux)',
     linuxWebkitSmoothScrollDesc: 'An: mit Nachlauf. Aus: zeilenweise wie in GTK-Apps.',
-    discordAppleCovers: 'Cover über Apple Music für Discord laden',
-    discordAppleCoversDesc: 'Sendet Künstler- und Albumname an die Apple-Such-API, um Cover für dein Discord-Profil zu finden. Standardmäßig aus Datenschutzgründen deaktiviert.',
+    discordCoverSource: 'Cover-Quelle',
+    discordCoverSourceDesc: 'Woher das Album-Cover für dein Discord-Profil geladen wird.',
+    discordCoverNone: 'Keine (nur App-Symbol)',
+    discordCoverServer: 'Server (über Album-Info)',
+    discordCoverApple: 'Apple Music',
     discordOptions: 'Erweiterte Discord-Optionen',
     discordTemplates: 'Benutzerdefinierte Textvorlagen',
     discordTemplatesDesc: 'Passen Sie an, welche Informationen in Ihrem Discord-Profil angezeigt werden. Variablen: {title}, {artist}, {album}',