Agent Skills: omni-bench

Develop the omni-bench benchmark framework (ASR/STT + text generation) built on a producer/scorer split with an open JSON spec as SSOT. Use when working in an omni-bench checkout — changing the JSON schemas, the prepare/producer/scorer/diff pipeline, the adapter seams (Transcriber / Generator), datasets, fixtures, or the Swift producer SDK; or when running and validating benchmark artifacts. Encodes the schema-evolution rules, determinism invariants, commands, and repo gotchas that are easy to get wrong.