Recording toolbar — idle
The first surface a user sees when they open the recorder. Status reads
"Ready", timer is 00:00, source picker shows the currently-selected
display, and a single primary "Start recording" button (red, with a static
white dot to telegraph what's about to happen) takes most of the visual
weight on the right.
This state is intentionally one-button. We don't want a "Pause" or "Stop" button visible before recording starts — they'd be muted and dead, which is worse than absent.