Publish to Maven Central with signing

[ericlmao]

Switch CI and Gradle publishing from the private Nexus to Maven Central and add artifact signing. Updates include:

• CI: rename workflow, import GPG key, set Gradle properties to use MAVEN_CENTRAL_* and GPG secrets, and keep release/snapshot publish steps.
• Root build.gradle: add signing plugin, update repository URLs/credentials for Sonatype, and configure signing for publications.
• Subprojects (moss-*, moss): add signing plugin, register sources and javadoc JAR tasks, attach those artifacts to the mavenJava publication, enrich POM metadata (description and SCM), and enable signing of the publication.

These changes enable signed uploads to Maven Central (Sonatype) and provide sources/javadoc artifacts and proper POM metadata for consumers.

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch snapshot

Tip

Issue Planner is now in beta. Read the docs and try it out! Share your feedback on Discord.

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}