Fix STT model display mismatch

[ComputelessComputer]

Summary

• Keep unavailable saved STT models visible in settings.
• Prevent settings from appearing to select a different local model.

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Note

Low Risk
Localized settings display/selection helper change with unit tests; no auth or data-path changes.

Overview
Fixes a display mismatch in AI transcription settings where the saved local/cloud model could differ from what the model dropdown showed (often the first downloaded model) even though the stored preference was unchanged.

The settings UI now derives displayedSttModel via getPreferredProviderModel with keepUnavailableSavedModel: true, so a saved model that is still known to the provider but not currently selectable (e.g. not downloaded) stays visible in the selector instead of being replaced silently. getPreferredProviderModel gains that option path; behavior without the flag is unchanged (still falls back to the first selectable model or clears).

Locale messages.po files were refreshed so Lingui source references track the small line shifts in stt/select.tsx.

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