CSS `zoom` re-lays-out and pixel-rounds each element, which opened ~1px seams
between map tiles (a faint grid over the map when zoomed). Switch the persistent
UI zoom to `transform: scale(z)` from the app root's top-left, with the root
counter-sized to (100/z)vw × (100/z)vh so it reflows to fill and scales back to
the window. transform scales the subtree as one composited layer, so tiles stay
seamless. Removed the now-unneeded tile-overlap CSS hack.
rouggy
34b60f9f20