refactor(01): align scaffold with Mythlane conventions (Kotlin DSL, CamelCase manifest, pinned server version)

- Convert build.gradle/settings.gradle to Kotlin DSL matching VotePipe + myth_*
- Manifest keys: lowercase -> CamelCase (Group/Name/Version/Main/ServerVersion/...)
  matching production Mythlane plugins (empirical authority)
- gradle.properties adopts pluginGroup/pluginVersion/pluginDescription/hytaleServerVersion
- Template manifest via processResources.expand(${version}, ${description}, ${hytaleServerVersion})
- Add baseline deps: gson (relocated), jetbrains annotations, JUnit 5
- shadowJar archiveBaseName=hytale-gravity-flip

Rebuild: BUILD SUCCESSFUL, fat JAR regenerated with CamelCase manifest.

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.14-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.4.1-bin.zip
 networkTimeout=10000
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME