Make Java SDK Maven publication releasable

[longquanzheng]

Summary

• make sdk-java publish a standard library JAR with complete Maven metadata
• package and load Rust BlobCache JNI libraries for supported Linux, macOS, and Windows targets
• validate publication contents and consume the staged artifact from independent Gradle and Maven projects
• update the Java SDK release workflow, Gradle wrapper, documentation, and ignore rules
• remove obsolete Java SDK implementation and generated OpenAPI sources that should not ship in the rewritten SDK

Why

The Java SDK publication path could produce an unusable Maven artifact and did not validate native BlobCache loading from a consumer project. This change makes the release workflow fail early on missing credentials, malformed artifacts, or unsupported publication contents.

User impact

Java users receive a conventional Maven library artifact whose runtime dependencies, metadata, and platform-specific JNI resources work from both Gradle and Maven consumers.

Validation

• ./gradlew test --no-daemon
• ./run-integration-tests.sh
• ./validate-publication.sh 0.0.2-local
• ./gradlew validatePublication --no-daemon
• make copyright-check
• actionlint .github/workflows/sdk-java-ci.yml .github/workflows/sdk-java-publish.yml
• shellcheck sdk-java/validate-publication.sh
• bash -n sdk-java/validate-publication.sh
• git diff --check origin/main...HEAD