Stats charts now handle empty states and remember your date range

Two improvements to the stats dashboard that you'll feel right away.

First, every chart now renders a proper empty state when there's no data in the selected range. Before, an empty chart looked broken — a flat baseline, no axis context, nothing to tell you whether the data was missing or the chart was loading. Now you see a clear "no activity in this range" message instead.

Second, the selected date range now persists in the URL. That means three things:

• Refreshing the page keeps your filter.
• You can share a stats URL with a specific date range and it'll load that range for the recipient.
• The browser back button works the way you'd expect.

Both small in scope, both big in everyday quality of life if you live in the stats dashboard.