- Status group headers ("Not Started (37)") stick under the top nav while
scrolling through their group, on every screen size
- On desktop the column header and filter rows stick beneath the group
header (table wrappers no longer clip them; these fixed-layout tables
never scroll sideways at desktop widths)
- layout.js measures the nav, group header and header row heights so the
sticky rows stack without gaps, re-measuring on re-render/resize/scroll
- Phones: the Advanced/Simple View button sits on its own line under the
device name instead of floating over the dialog content
- Rename mobile.css/js to layout.css/js now that they hold desktop rules
