Start the kiosk faster, with no white screen

Operator stations showed a long white screen while the kiosk started, and an update that could not be installed left the station without its window until a restart.

• Improved kiosk startup: the window now appears only once the operator UI is drawn, in your system's light or dark colour, and the UI is ready up to 7x sooner on macOS (from 4.8 s to under 0.7 s on a Mac with Screen Time web filtering)
• Fixed stations that lost their kiosk window after a failed update; a window that crashes now reopens immediately, and the station no longer waits for the window before it connects
• Improved operator UI loading: 20% less code to start, with prompt controls, menus and run details loaded when first needed, and a recovery screen instead of a blank page if the UI hits an error