Clearer dashboard metrics

The metric tiles on your Dashboard now explain themselves:

• Every tile states its period ("Last 30 days") and, where relevant, how long purchases are counted after watching.
• Watcher tiles show how they compare to your store average (for example "3.9x store average").
• "Saw a video" shows what share of shoppers who loaded a widget actually saw your videos.
• Up/down changes are only highlighted in green or red when the change is meaningful, so small day-to-day noise doesn't look like bad news.
• Tiles show a loading skeleton while data loads, and a dash instead of a misleading $0 when there is no data yet.