The webview focuses a clicked button and the focus stays there: across
project window-tab switches, and popups hand it back to their trigger. The
next keystroke switches the engine to keyboard modality, so that button got a
focus ring (window tabs, the title-bar project switcher). A pressed control is
now marked and keeps no ring until Tab or an arrow key moves focus onto it.
Focus itself is unchanged, since actions resolve their context from it.
Closes#1211
