fix: Qt threading crash and custom hotkey support

- Fix crash when pressing hotkey caused by Qt threading issue
- Use Qt Signal/Slot mechanism for cross-thread UI updates
- Add custom hotkey capture with modifier-only support (e.g., Ctrl+Win)
- Add hotkey validation on backend
- Bump version to 1.3.1

chore : cleanup

fix: model download HuggingFace link and add clear cache option

- Fix "Download from HuggingFace" button using api.openExternalUrl() instead of window.open() which doesn't work in Pyloid/QtWebEngine
- Add clear_model_cache() method to ModelManager for deleting only faster-whisper models
- Add clear_model_cache RPC endpoint in server.py
- Add clearModelCache() API method in api.ts
- Add "Delete AI Models" checkbox option in Settings danger zone dialog
- Only deletes VoiceFlow's faster-whisper models, not other HuggingFace cached models

feat: expand model support with all faster-whisper variants

- Add all faster-whisper models: English-only (.en) and distilled variants
- Add detailed model metadata (speed/accuracy ratings, sizes, descriptions)
- Update turbo model to use official Systran repo
- Fix TypeScript type error in ModelDownloadProgress onComplete callback
- Enhance Onboarding model selection with category info and best-for guidance
- Bump version to 1.2.1

chore: bump version to 1.2.0 for custom hotkeys release

feat: Implement core application structure, UI pages, and Python back…

…end services for voice flow functionality.

feat: Introduce core UI components for home page, settings management…

…, and stats display.

feat: Add PyInstaller build script for VoiceFlow application with pla…

…tform-specific configurations and optimization.