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/README.md

@@ -16,7 +16,7 @@ subsystem, how they fit together, and the end-to-end flows that tie them.
 | [commands.md](commands.md) | Commands — message & slash commands, dispatch, options |
 | [tasks.md](tasks.md) | Tasks — button/emoji/modal/step/built-in/persistable/scheduled tasks |
 | [persistence.md](persistence.md) | Database — Hibernate/JPA, Flyway, entities, repositories, services |
-| [music.md](music.md) | Music — Lavaplayer pipeline, queue, custom Udio source |
+| [music.md](music.md) | Music — Lavalink node & client, queue, event dispatch |
 | [web-api.md](web-api.md) | HTTP Web API — internal control & introspection server |
 | [threading.md](threading.md) | Threading & scheduling infrastructure |
 | [utilities-and-bootstrap.md](utilities-and-bootstrap.md) | Utilities, configuration, logging, exceptions |