Fix the hosted Java selector for 1.21.1 releases

[SkyBlade1978]

Summary

• keep java_toolchain_version=21.0.7+6 as the exact Temurin compiler/runtime identity
• add java_setup_version=21.0.7+6.0.LTS, the catalog selector now required by actions/setup-java
• add a regression contract that requires both values and prevents them being conflated

Cause

Release run 33608622984 routed and validated 4.0.16.121011 correctly, then failed before Gradle started because GitHub's Temurin catalog no longer matched the shorter 21.0.7+6 selector. The catalog lists that same build as 21.0.7+6.0.LTS.

The shared dispatcher already supports a separate hosted setup selector, so this branch metadata change uses that intended seam without loosening the pinned toolchain or changing older Java pipelines.

Validation

• ReleaseWorkflowContractTest passed under the pinned Java 21/8/25 toolchains
• verifyReleaseConfiguration passed
• git diff --check passed
• the failed release created no tag and did not enter Maven, CurseForge, or GitHub publication

No production source, gameplay behavior, API/schema, artifact name, or release content changes.