Bootstrap java lcod-run skeleton #2
Description
Stand up the new Gradle project for the Java kernel so we can ship a runnable fat-jar and embedding API.\n\nAcceptance criteria\n- Gradle wrapper available (Java 21 toolchain pinned, auto-download for CI).\n- CLI skeleton exposes the same surface as lcod-run (compose/input/cache flags, log level, timeout).\n- Public API exposes configuration + runner classes for embedding.\n- Tests/DCI pipelines run via ./gradlew test.