Add responsive design and mobile support

[superposition]

Description

Make the web app work well on all screen sizes.

Tasks

• Add responsive breakpoints (mobile, tablet, desktop)
• Stack panels vertically on mobile
• Make surface viewer full-width on mobile
• Add collapsible panel sections
• Implement touch gestures for surface rotation
• Add pinch-to-zoom for mobile
• Test on various screen sizes
• Add viewport meta tag

Acceptance Criteria

• Usable on mobile devices
• Touch gestures work smoothly
• No horizontal scrolling on mobile

Labels

web-app, frontend, mobile