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>

CHANGELOG.md

@@ -16,6 +16,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [1.46.0] - 2026-05-05
 
+## Added
+
+### Discord — album cover art from your own server
+
+**By [@Sayykii](https://github.com/Sayykii), PR [#462](https://github.com/Psychotoxical/psysonic/pull/462)**
+
+* Discord Rich Presence can now show **album artwork from your own server** via the Subsonic `getAlbumInfo2` endpoint (requires the server to be publicly reachable).
+* New cover-source picker under Discord Rich Presence settings: **None** (app icon only), **Server**, or **Apple Music**. Mutually exclusive.
+* Fresh installs default to **Server** for opt-in-friendly cover art with no third-party data leak. Existing users keep their previous Apple-covers preference via migration.
+
 ## Changed
 
 ### Dependencies — npm / Cargo refresh and rodio 0.22