Promote UnlinkPool case to build green

[Th0rgal]

Summary

• promote unlink_xyz/pool to stage build_green with translation_status translated
• clear unsupported_feature_codes in the case and build_green task manifests
• update review/proof notes and generated benchmark metadata for the promoted case

Verification

• git diff --check
• lake build Benchmark.Cases.UnlinkXyz.Pool.Compile Benchmark.Generated.UnlinkXyz.Pool.Tasks.BuildGreen
• python3 scripts/validate_manifests.py
• python3 scripts/generate_metadata.py --check
• python3 scripts/check_reference_solutions.py

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Note

Low Risk
Mostly manifest/metadata and documentation updates that mark unlink_xyz/pool as buildable; risk is limited to benchmark inventory correctness and CI expectations.

Overview
Promotes the unlink_xyz/pool benchmark case from scoped to build_green, updating its translation_status to translated and clearing unsupported_feature_codes in both the case and build_green task manifests.

Updates the generated task template and reference proof placeholder comments to reflect the new build-green target, and regenerates benchmark metadata (REPORT.md, benchmark-inventory.json) so the case is counted as buildable/active with no remaining non-buildable active cases.

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