Routing preview reflects the per-language transcription preference

The Spanish transcription preference applied to requests but not to GET /v1/routing/preview, so the console key wizard listed and pinned the global ranking instead. A key created that way was pinned to an order that then outranked the preference on every request it made.

The preference is now applied wherever a candidate order is produced: buffered transcription, streaming transcription, and the routing preview. Previously it applied only to the streaming socket.

For Spanish, the preview now returns ElevenLabs first and Soniox second. The console builds its override list from this response, so a key created with Spanish selected pins that order rather than the global one.

It remains a preference and not a restriction: a provider that cannot serve the request is skipped, the rest of the ranking keeps its order behind it, and a language with no entry is unaffected.

The preference is keyed on the base language, because transcription is accent-independent: es, es-CO and es-419 all resolve to the same order.

Action: No migration is required. Keys created before this change carry the pinned order they were created with; recreate a key, or unpin its transcription stage, to follow the preference.