migrated to Gradle and Minestom 2026.10.05-26.2

- Maven -> Gradle 9.6.1 (shadow 9.6.1, Java 25), shadow jar is build/libs/limbo.jar
- Minestom from Maven Central (net.minestom:minestom), speaks Minecraft 26.2 natively
- Velocity forwarding via Auth.Velocity; the secret is no longer hardcoded but read from
  forwarding.secret in the working directory or VELOCITY_FORWARDING_SECRET
- time rate via defaultClock().pause() (new clock API)
- slf4j-simple for logging (Minestom no longer ships a logger)
- removed target/ and Maven files from the repository
- uploadLimbo task copies the jar to the limbo server

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.6.1-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists