Voice mode: add multilingual support (French transcription is poor)

Summary

Voice mode (/voice, push-to-talk with Space) works great for English but produces very poor transcription for French. Since Claude itself handles French perfectly, the bottleneck is the speech-to-text layer.

Environment

• Fedora 43 (Sway/Wayland)
• PipeWire 1.4.8
• sox installed, mic working correctly
• Claude Code latest (auto-updates enabled)

Steps to reproduce

1. Enable voice mode (voiceEnabled: true in settings)
2. Hold Space and speak in French
3. Observe garbled/incorrect transcription

English speech in the same setup transcribes correctly.

Expected behavior

Voice mode should support major languages (at minimum French, Spanish, German, etc.), either via:

• A voiceLanguage setting in settings.json
• Automatic language detection (Whisper supports this natively)

Impact

This effectively makes voice mode English-only, which limits its usefulness for non-English-speaking developers who otherwise use Claude in their native language daily.