Revaulting

Remove NBT-API and migrate to Paper API
Replaced NBT-API with equivalent Paper API calls for Vault reward data.
Storage and behaviour remain the same; dependency removal improves maintainability and compatibility.

Migrate build to Kotlin DSL and add version catalogue
Moved from Groovy build.gradle to Kotlin DSL with libs.versions.toml.
Centralised versions, bumped to 0.3.0, and modernised build configuration including shadowJar and runPaper.

Revamp README and update description
Reorganised README with clearer sections and added a bStats badge.
Simplified paper-plugin.yml description to a single concise line.