fix(maps): zooming stays centred on the grid and decode maps

The hard maxBounds added for the single-world look fought the zoom: with
the world smaller than the window the clamp dragged every zoom step into
a corner. The noWrap tiles already guarantee one world on their own, so
the bounds go — on both maps.

frontend/src/components/GridSquareMap.tsx

@@ -128,15 +128,11 @@ export function GridSquareMap({ myGrid, className }: { myGrid?: string; classNam
       // impossible on any window wider than it is tall: one step out was already
       // too far in.
       minZoom: 0,
-      maxBoundsViscosity: 1, // don't let a drag slide the world off to one side
+
     }).setView([20, 0], 2);
     // The whole world, once, whatever the window is shaped like — computed by
     // Leaflet from the container rather than guessed with a zoom number.
     m.fitWorld({ animate: false });
-    // Latitude only: the poles are the edge of the projection and there is
-    // nothing beyond them, while leaving longitude free keeps a drag from
-    // fighting the operator near the date line.
-    m.setMaxBounds(L.latLngBounds(L.latLng(-85, -Infinity), L.latLng(85, Infinity)));
     mapRef.current = m;
     layerRef.current = L.layerGroup().addTo(m);
     // Leaflet measures its container ONCE, when the map is created, and never