Add Fabric 1.21.11 support

[IuCC123]

Summary

• update the mod to target Minecraft 1.21.11 with Yarn 1.21.11+build.3 and Fabric API 0.139.5+1.21.11
• update fabric.mod.json to advertise 1.21.11 compatibility
• replace the removed MultilineText alignment draw usage with centered per-line rendering so the confirmation screen still compiles and renders correctly

Testing

• GRADLE_USER_HOME=/tmp/songplayer-gradle ./gradlew build