Release IronAgeFurniture Phase 3 for Forge 1.12.2

[SkyBlade1978]

Summary

• bring the Forge 1.12.2 branch to the Phase 3 lighting feature set and 0.3.0.112021 release identity
• add all sixteen padded-bench colours without adding registry IDs or changing the established joining algorithm
• fix recipe advancements, optional integration conditions, flammability, and lava-lamp behavior
• modernize the reproducible ForgeGradle 7 build, CI, release artifacts, and Eclipse setup
• expose small namespace-safe extension points for future furniture add-ons

Verification

• clean check and build
• Javadoc and all catalog, resource, metadata, namespace, Maven, repository, and workflow audits
• 7,887 JSON documents and 2,516 exact recipe advancements validated
• deterministic three-jar release bundle and SHA-256 verification
• prepared release bundle and Eclipse production classpath verification
• manual gameplay acceptance completed