Publish sources and javadocs for Nexus artifacts

[ericlmao]

Summary

• Enable sourcesJar and javadocJar for both published modules.
• Attach the documentation artifacts to the Maven publication so Nexus receives them with the shaded main jar.
• Fix common Javadoc doclint issues so publication can complete cleanly.

Testing

• common:javadoc and paper:javadoc pass locally.
• common:sourcesJar, common:javadocJar, paper:sourcesJar, and paper:javadocJar build successfully.
• publishToMavenLocal confirms both modules publish jar, sources, javadoc, pom, and Gradle module metadata artifacts.