//! Backend presets. Every supported transcription server speaks the same
//! OpenAI-compatible multipart `/audio/transcriptions` shape, so a "provider"
//! is just a label + the defaults ([`crate::Endpoint`] carries the actual
//! URL / auth / model). Adding a backend = adding a variant here and a
//! constructor on `Endpoint` — see `.claude/skills/add-endpoint-adapter`.
/// A known transcription backend.