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/zh.ts

@@ -691,8 +691,11 @@ export const zhTranslation = {
     linuxWebkitSmoothScrollDesc: '开：惯性滚动。关：逐行，类似 GTK。',
     discordRichPresence: 'Discord Rich Presence',
     discordRichPresenceDesc: '在 Discord 个人资料上显示当前播放的曲目。需要 Discord 处于运行状态。',
-    discordAppleCovers: '通过 Apple Music 为 Discord 获取封面',
-    discordAppleCoversDesc: '将艺术家和专辑名称发送至 Apple 搜索 API，以为 Discord 个人资料查找封面图片。出于隐私考虑，默认禁用。',
+    discordCoverSource: '封面来源',
+    discordCoverSourceDesc: '从何处获取 Discord 个人资料上显示的专辑封面。',
+    discordCoverNone: '无（仅显示应用图标）',
+    discordCoverServer: '服务器（通过专辑信息）',
+    discordCoverApple: 'Apple Music',
     discordOptions: 'Discord 高级选项',
     discordTemplates: '自定义文本模板',
     discordTemplatesDesc: '自定义在 Discord 个人资料上显示的信息。变量：{title}, {artist}, {album}',