A timestamped run on OpenRouter always asked openai/whisper-1 for the
segments, whatever model was picked for plain transcription. Not every
model there returns segment times, so the one to use is now its own
setting, openrouter_subtitle_model, shown in the speech-to-text box only
when OpenRouter is the provider. Empty keeps the old whisper-1 fallback.
Target carries the choice as subtitle_model and timestamp_model() reads
it; the other providers are unchanged.