Responsive/Mobile: Fix hardcoded heights and add breakpoints

[samkeen]

Summary

Improve responsive design for better mobile/tablet experience.

Tasks

• Remove hardcoded max-h-[600px] in session-tabs conversation view - should be responsive
• Add mobile breakpoints to grid layouts:
  • Session detail 4-col grid needs sm: and md: breakpoints
  • Activity timeline 7-col grid is too wide on tablets
• Fix table overflow on mobile (projects table)
• Modals should use full width on small screens (max-w-full sm:max-w-md)
• Activity timeline bar chart h-32 should adapt to mobile

Files to update

• components/session-tabs.tsx (line ~65: max-h-[600px])
• components/activity-timeline.tsx (grid and height issues)
• app/page.tsx (table overflow)
• components/settings-modal.tsx
• components/project-config-modal.tsx