Root cause: Leaflet 1.9.4's Map.closePopup() never nulls map._popup (only
unbindPopup does), so the moveend guard 'if (map._popup) return' skipped
every overlay reload forever after the first popup was ever opened. Opening
one camera popup froze the marker layer: zoom out and the map kept showing
the stale zoomed-in subset (or nothing) until a full page refresh.
Track real popup state via popupopen/popupclose events instead, and close
the popup on user zoom/drag so the moveend reload always runs after
navigation; the autopan skip still protects the popup when it pans itself
into view.
