Accessibility: make interactive map circles keyboard reachable #185

What

InteractiveMap's existing Leaflet circle markers bind tooltips and popups but do not expose keyboard focus or activation. Keyboard users can pan/zoom and switch overlays, but cannot reach a nursery/adult-capture circle to inspect its details or follow the nursery link in its popup.

This predates the current map PRs. The #178 review adds keyboard controls to the new move polylines and arrow-key reading to the SVG fallback; this issue records the separate pre-existing circle-marker gap under #70.

Why

Pointer-only map details leave keyboard users without an equivalent way to inspect locations, even though the SVG fallback now has the shared chart controls.

Acceptance

• Circle details are reachable and operable with the keyboard after Leaflet mounts.
• Focus visibly identifies the selected circle; its label/details are available to assistive technology.
• Popup links remain reachable, and Escape dismisses details without trapping focus.
• Controls survive season redraws, zoom redraws, and overlay toggles.
• Add a synthetic-data browser regression for nursery and adult circles.