feat: add PWA support and mobile UI improvements

[athal7]

Summary

• PWA support with service worker caching and web manifest
• Mobile UI improvements for iOS/Android browsers
• Touch-friendly controls and keyboard handling

Features

• Service worker with intelligent caching (stale-while-revalidate)
• Web app manifest for installable PWA experience
• iOS meta tags and safe area inset support for notched devices
• Virtual keyboard detection for proper layout adjustments
• Project reordering via move up/down menu options on mobile
• Scroll-to-bottom button when not at conversation end

Related Issues

• Closes #5126 - Mobile-friendly web UI
• Relates to #6536 - Mobile App feature request
• Relates to #6200 - Message box overflow on mobile viewports
• Relates to #7530 - Cannot type in terminal on mobile browser
• Relates to #6257 - Easier scrolling (scroll-to-bottom button)

Demo

Before

https://github.com/user-attachments/assets/6ac2c8c7-f6d8-4e45-bac1-c5af17bfda97

After

https://github.com/user-attachments/assets/8e4f286a-84ab-4e2d-9e06-60a60b5fbd01