Support hosted Java selectors in the release dispatcher

[SkyBlade1978]

Summary

• read an optional java_setup_version from target metadata
• use that hosted-catalog selector for both immutable builds and Maven publication
• preserve java_toolchain_version as the branch's exact Gradle/runtime contract
• fall back to the existing toolchain value when older branches do not define the new property
• reject a hosted selector whose Java major does not match the declared toolchain

Why

The Forge 1.20.6 release run failed before Gradle because Temurin publishes the exact 21.0.7+6 build to actions/setup-java as 21.0.7+6.0.LTS. The project correctly identifies the runtime as 21.0.7+6, so those two representations need separate metadata.

Failed run: https://github.com/MinecraftModDevelopmentMods/OreSpawn/actions/runs/33522096942

Validation

• actionlint 1.7.12 passes for deploy-release.yml
• routing/setup contracts pass for representative Java 8, Java 17, and Java 21 branches
• Java 8/16 plus Gradle 17 split-runtime behavior is unchanged
• branches without java_setup_version retain the old behavior

This PR creates no tag and performs no publication. The matching 1.20.6 metadata PR must also merge before retrying the release.