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/en.ts

@@ -715,8 +715,11 @@ export const enTranslation = {
     useCustomTitlebarDesc: 'Replace the system title bar with a built-in one that matches the app theme. Disable to use the native GNOME/GTK title bar.',
     linuxWebkitSmoothScroll: 'Smooth wheel (Linux)',
     linuxWebkitSmoothScrollDesc: 'On: inertial scroll. Off: line-by-line, GTK-style.',
-    discordAppleCovers: 'Fetch covers from Apple Music for Discord',
-    discordAppleCoversDesc: 'Sends the artist and album name to Apple\'s search API to find cover art for your Discord profile. Disabled by default for privacy.',
+    discordCoverSource: 'Cover art source',
+    discordCoverSourceDesc: 'Where to fetch album artwork shown on your Discord profile.',
+    discordCoverNone: 'None (app icon only)',
+    discordCoverServer: 'Server (via album info)',
+    discordCoverApple: 'Apple Music',
     discordOptions: 'Advanced Discord options',
     discordTemplates: 'Custom text templates',
     discordTemplatesDesc: 'Customize what information is shown on your Discord profile. Variables: {title}, {artist}, {album}',