- Add vosk_model_size and whisper_model_size to config to track model
selection independently for each engine
- Update config manager with get_model_size_for_engine() and
set_model_size_for_engine() methods for per-engine model tracking
- Add automatic migration for existing configs without per-engine model sizes
- Update settings dialog to use engine-specific model sizes when populating
model options
- Update install.sh to include new per-engine model fields in default config
- Fix: Previously, switching from VOSK to Whisper would incorrectly try to
download the recommended model instead of the previously used model
Fixes the issue where switching back to Whisper after using VOSK would
start downloading the medium model instead of remembering the tiny model
that was configured during installation.