📱 Mobile and tablet experience improvements

• Progressive loading of conversations and agents lists • Smooth conversation scrolling with virtualized message lists • Optimized performance for conversations with thousands of messages • Bigger touch targets for mobile-friendly interactions • Fixed mobile layouts for agent builder and conversation views • Smart keyboard handling that prevents unexpected pop-ups • Proper iOS status bar colors and theming • Touch-friendly interactions with disabled hover effects on mobile • Resizable panels that work correctly on mobile screens