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/nl.ts

@@ -696,8 +696,11 @@ export const nlTranslation = {
     linuxWebkitSmoothScrollDesc: 'Aan: traag naloop. Uit: regel voor regel, GTK-stijl.',
     discordRichPresence: 'Discord Rich Presence',
     discordRichPresenceDesc: 'Toont het huidige nummer op je Discord-profiel. Discord moet daarvoor geopend zijn.',
-    discordAppleCovers: 'Hoezen ophalen via Apple Music voor Discord',
-    discordAppleCoversDesc: 'Stuurt artiest- en albumnaam naar de Apple-zoek-API om een hoes te vinden voor je Discord-profiel. Standaard uitgeschakeld vanwege privacy.',
+    discordCoverSource: 'Hoesbron',
+    discordCoverSourceDesc: 'Waar de albumhoes voor je Discord-profiel vandaan komt.',
+    discordCoverNone: 'Geen (alleen app-icoon)',
+    discordCoverServer: 'Server (via albuminfo)',
+    discordCoverApple: 'Apple Music',
     discordOptions: 'Geavanceerde Discord-opties',
     discordTemplates: 'Aangepaste tekstsjablonen',
     discordTemplatesDesc: 'Pas aan welke informatie wordt weergegeven op je Discord-profiel. Variabelen: {title}, {artist}, {album}',