Move pure utility functions from app-store.ts and type files into
dedicated utils modules for better separation of concerns:
- theme-utils.ts: Theme and font storage utilities
- shortcut-utils.ts: Keyboard shortcut parsing/formatting
- usage-utils.ts: Usage limit checking
All utilities are re-exported from store/utils/index.ts and
app-store.ts maintains backward compatibility for existing imports.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
