Switch from fixed 48-column grid to responsive breakpoints:
- lg (>=1200px): 48 columns, free positioning (unchanged desktop behavior)
- md (>=900px): 24 columns, vertical compaction
- sm (>=600px): 12 columns, vertical compaction
- xs (<600px): 6 columns, vertical compaction
Widgets automatically reflow and stack on smaller screens instead of
being squished. Layout changes are only persisted from the desktop
breakpoint. Drag/resize editing is desktop-only.
Also adds mobile CSS refinements for topbar, tabs, and workspace padding.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude