Introduce Expo QR code functionality to allow users to preview their projects on mobile devices. Added a new QR code modal component, integrated it into the chat and preview components, and implemented Expo URL detection in the shell process. This enhances the mobile development workflow by providing a seamless way to test Expo projects directly on devices.
- Clean up and consolidate Preview icon buttons while removing redundant ones.
- Reduce gap between elements in BaseChat component from `gap-4` to `gap-2`
- Remove bottom margin from AssistantMessage component for cleaner layout
- Add expo.svg icon to the icons directory for future use
