Remove Lavaplayer and migrate to Lavalink

Replaced the bot's audio handling system by removing Lavaplayer dependencies and migrating to a Lavalink v4 node. Updated `MusicManager`, `TrackScheduler`, and related classes to utilize the `LavalinkClient`. Refactored playlist and track loading logic, task integrations, and event dispatch to integrate with the remote node. Deprecated the custom Udio source, preserving references for a future plugin port. Documented configuration and deployment details for the new audio architecture.

docs/reference/udio-lavalink-plugin/README.md

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+# Udio source — follow-up reference
+
+These files are **not part of the build**. They are the original client-side Lavaplayer
+implementation of the udio.com source, kept verbatim as the reference for a future port.
+
+| File | Was |
+|---|---|
+| `UdioAudioSourceManager.java` | `me.bobert.netneutrality.music.source.UdioAudioSourceManager` |
+| `UdioAudioTrack.java` | `me.bobert.netneutrality.music.source.UdioAudioTrack` |
+| `UdioAudioSourceManagerTest.java` | its unit test |
+
+## Why they were moved
+
+The bot no longer decodes audio itself: after the [migration to Lavalink](../../music.md), source
+resolution happens on the node. A Lavaplayer `AudioSourceManager` living in the bot process can
+never be used by Lavalink, and these classes cannot even compile now that the `dev.arbjerg:lavaplayer`
+dependency has been dropped from `pom.xml`.
+
+## Status
+
+**Udio playback is disabled.** `SourceFinder` still classifies Udio URLs, but
+`SourceFinder.getIdentifier` returns no identifier for them and `MusicManager.play` replies that
+Udio is temporarily unsupported.
+
+## Follow-up
+
+Port `UdioAudioSourceManager` / `UdioAudioTrack` into a standalone **Lavalink server plugin**
+(its own build and published artifact), then enable it by adding the dependency to
+`lavalink/application.yml`:
+
+```yaml
+lavalink:
+  plugins:
+    - dependency: "<group>:udio-plugin:<version>"
+```
+
+Once the node resolves `https://www.udio.com/songs/...` identifiers, the only bot-side change is to
+restore `Udio` in the `SourceFinder.getIdentifier` switch and drop the "temporarily unsupported"
+reply in `MusicManager.play`.
+
+The scraping logic itself still applies: the manager extracts metadata and a direct playback URL
+from the Next.js payload (`self.__next_f.push(...)`) of the track page, and the URL must be
+re-fetched right before playback because it expires.