Prepare linter-core for Maven Central release #56

Make dsf-linter Maven Central-ready so linter-core can be consumed by dsf without custom repositories.

Tasks

• Add/verify required POM metadata (url, developers, scm, license info).
• Configure maven-source-plugin to publish sources.jar.
• Configure maven-javadoc-plugin to publish javadoc.jar.
• Configure maven-gpg-plugin for artifact signing (release flow).
• Validate linter-core builds as a releasable artifact (jar, sources, javadocs, signatures).

Acceptance Criteria

• linter-core produces jar, -sources.jar, -javadoc.jar, and .asc signatures.
• POM metadata meets Maven Central requirements.
• Release pipeline is ready for first Central publication.