v2.3: Major refactoring, Lavalink music system, Spotify support, CI/CD

- Full refactoring: max 200 lines/file, max 3 files/dir, KISS/DRY/SOLID
- Lavalink client 3.4.0 + LavaSrc plugin (Spotify, Apple Music, Deezer)
- 3-bot architecture: main (!), music (q!), radio (r!)
- Filters: bassboost, nightcore, vaporwave, equalizer
- Slash commands for music (/play, /skip, etc.)
- Persistent queue in SQLite, auto-leave timer
- Radio manager with auto-reconnect
- Custom welcome GIF greetings via nekos.life
- JDA 5.6.1, gson 2.14, hikaricp 6.3, all deps updated
- Fixed YouTube playback via ytmsearch (LavaSrc)
- CI/CD: Docker publish + release workflows
- SpotBugs: all real bugs fixed, ignoreFailures=false
- Checkstyle: Google Style (adapted), 0 violations

Dockerfile

@@ -9,8 +9,7 @@ FROM eclipse-temurin:21-jre-alpine
 RUN addgroup -S bot && adduser -S bot -G bot
 WORKDIR /app
 COPY --from=builder /build/build/libs/discord-bot-1.0.0.jar app.jar
-COPY --from=builder /build/data/ ./data/
-RUN mkdir -p /app/data && chown -R bot:bot /app
+RUN mkdir -p /app/data /app/logs && chown -R bot:bot /app
 USER bot
 VOLUME /app/data
 EXPOSE 8712