A clearer device detail page and SMS charts

The dashboard grows up a little. Every device gets its own detail page worth opening, and the charts finally show you something useful.

What's new

• Redesigned device detail page — phone identity, status, recent activity, and per-device message history in one place.
• "Last activity" timestamps across the device list so you can spot a sleeping phone at a glance.
• SMS charts on the dashboard now show sent and received volumes over time, not just totals.
• A pile of small UI fixes to the device and phone lists, including better empty states.