Shrink monitor to fraction of its size and centre it inside
the original. fraction is clamped to [0.1, 1.0]. Used to size
the BreakDelivery::Windowed overlay so the desktop stays
clickable around it.
Surface a break through whichever channel the active settings ask
for: a system notification or the overlay (full-screen or windowed).
Notification delivery short-circuits the overlay path entirely.
Build a BreakEvent, stash it in current_break, position an
overlay window on each selected monitor, and emit break:start to
the renderer. Used directly for sleep/resume-last paths; normal
scheduled breaks go through deliver_break instead.
Human-friendly break duration for notifications (e.g. "20 seconds",
"5 minutes", "1m 30s"). Drops the seconds part when the
duration is a whole-minute multiple.
Index of the monitor that contains (cursor_x, cursor_y), or
None if the cursor sits outside every rect. Used by
MonitorPlacement::Active to decide which display the overlay
should pop on.