Non-European languages (incl. Chinese) are undiscoverable on the default Parakeet engine

[ruzin]

Problem

The transcription Language picker (Settings → AI) is engine-dependent: AiTab.tsx uses engine === 'whisper' ? LANGUAGES_WHISPER : LANGUAGES_PARAKEET. Parakeet TDT v3 is a ~25-language European model, so non-European languages — including the new Chinese (Simplified/Traditional) options from #102 — only appear when the engine is set to Whisper.

Since the app defaults to Parakeet, a user who wants Chinese (or any non-European language) has no visible path to it: the options simply aren't in the dropdown, and nothing tells them they need to switch the transcription engine to Whisper first. They'd get poor/empty results on Parakeet with no explanation.

Impact

• Chinese users (the audience feat: enhance Chinese language support with variant handling and conversion #102 was built for) can't find the feature unless they already know to switch engines.
• Same for any Whisper-only language (Japanese, Korean, Thai, Arabic, etc.).

Proposed fix (small, no new dependency)

Make the language↔engine relationship discoverable. Options, roughly in order of preference:

1. Auto-route on selection — show all languages regardless of current engine; if the user picks a Whisper-only language while on Parakeet, auto-switch the engine to Whisper (with a small inline note: "Chinese needs the Whisper engine — switched for you").
2. Prompt — surface the Whisper-only languages in the list but, on selection under Parakeet, confirm the engine switch.
3. Hint — a note under the Language row when on Parakeet: "Chinese, Japanese, and other non-European languages require the Whisper engine."

This is renderer-side (the picker + engine setter already exist); no backend or dependency changes.

Context

Surfaced during the #102 (Chinese Simplified/Traditional) review. #102 correctly keeps Chinese in the Whisper-only list — this issue is purely about discoverability/routing.

Labels: enhancement, ux