Rename "List Density" to "Density" and apply spacing changes globally
instead of only to email list item heights.
- Replace hardcoded padding/gap values with CSS custom properties
(--density-item-py, --density-item-gap, --density-header-py,
--density-card-p, --density-sidebar-py) set via JS on :root
- Apply density-responsive spacing to email list items, thread views,
email viewer, sidebar, navigation rail, contacts, and calendar
- Use inline styles instead of Tailwind arbitrary value classes to
avoid Turbopack compilation hangs
- Rename listDensity → density in store, types, and components
- Add persist migration (v1 → v2) and onRehydrateStorage callback
- Update all 8 locale files with broadened labels/descriptions