New: a collapsible Stats section at the top of the popup. It shows total requests and since when, how many roots cover 90% and 99% of your requests, the share of the top 3 roots, roots under 1%, the share not trusted by default (roots not built in and certificate exceptions), and requests by CA operator.

Changed:
- Seen roots are sorted by request count, most used first. Copy still lists them by name.
- The popup grows to 90% of the window height, and the root list fills the extra space.
- Reset and Copy moved up next to Update list. Reset is now "Reset seen", so it can't be mistaken for resetting the downloaded Mozilla list.
- "Built-in roots" is now "Seen built-in roots", so it can't be mistaken for the full list of built-in roots next to "Never seen".
- Clearer extension description.