Coverage gap detection

On any site's edit page, set "Min guards on duty" (e.g. 1 or 2) and a "Staffing window" (e.g. 22:00-06:00 for overnight, blank for 24/7).

The schedule samples each site's window at 15-minute slots. Whenever fewer than the required number of guards are concurrently scheduled, that interval counts as a gap. The banner above the grid surfaces total uncovered hours, sorted worst-first.

To fix a gap: add a shift in the affected window, or click "AI: auto-fill open shifts" in the toolbar to let the AI find guards for unfilled slots.