Sans-IO MPEG-1/2/2.5 Layer III ("MP3") elementary stream mux + demux.
Freestanding — no Mediaway types.
Unprefixed reusable core — naming [ADR-0012](../../docs/adr/0012-unprefixed-reusable-cores.md).
v1 scope: Layer III only (Layer I/II rejected, not misparsed). See
[`docs/roadmap.md`](docs/roadmap.md) and
[`adr/0001`](adr/0001-mpeg-audio-freestanding-core.md).