deps: react-leaflet 1.8 -> 4.2 (+ leaflet 1.9) — the last legacy react-* lib

Ground-up hooks rewrite of the app's core map. Removes the final batch of
React-19-blocking warnings (legacy context on Map/LayersControl/TileLayer/
Marker/CircleMarker/Circle/Tooltip + ReactDOM.render from the old controls).

Core: <Map> -> <MapContainer>; .leafletElement refs (6 files) -> the map/
layer instances directly, via a <MapReady> child (useMap) + plain refs on
Marker/Circle/GeoJSON; controlled viewport (onViewportChanged + state.center/
zoom) -> <MapEvents> (useMapEvents moveend/zoomend) + imperative setView;
onClick -> eventHandlers={{click}}; Path styling -> pathOptions/style;
subsUnion takes the L.Map directly.

The 4 v1-only plugins reimplemented (new in-repo helpers under Maps/):
- react-leaflet-control -> MapControl (L.Control + createPortal)
- react-leaflet-google  -> GoogleMutantLayer (createLayerComponent +
  leaflet.gridlayer.googlemutant; Google Maps API already loaded by Gkeys)
- react-leaflet-fullscreen -> createControlComponent + leaflet.fullscreen
- leaflet-sleep / leaflet-graphicscale kept as vanilla (work on leaflet 1.9)

Browser-verified: /fires (tiles, OSM+Google layer switch, custom control,
fullscreen, graphic scale, pan/zoom -> re-fetch, no NaN), fire detail
(GeoJSON rect + fitBounds), home (3 maps coexist; SelectionMap draggable
marker -> updatePosition + distance circle). Console now shows 0 React
warnings on home/fires. REST smoke byte-identical.

imports/ui/components/Maps/MapControl.js

@@ -0,0 +1,32 @@
+import { useEffect, useState } from 'react';
+import { createPortal } from 'react-dom';
+import { useMap } from 'react-leaflet';
+import L from 'leaflet';
+
+// Replacement for react-leaflet-control (v1-only): mounts a Leaflet control at
+// the given corner and portals arbitrary React children into it. Click/scroll
+// on the control no longer pans/zooms the map underneath.
+const MapControl = ({ position = 'topright', children }) => {
+  const map = useMap();
+  const [container, setContainer] = useState(null);
+
+  useEffect(() => {
+    const ReactControl = L.Control.extend({
+      onAdd: () => {
+        const div = L.DomUtil.create('div', 'leaflet-control leaflet-control-react');
+        L.DomEvent.disableClickPropagation(div);
+        L.DomEvent.disableScrollPropagation(div);
+        setContainer(div);
+        return div;
+      },
+      onRemove: () => setContainer(null)
+    });
+    const control = new ReactControl({ position });
+    control.addTo(map);
+    return () => control.remove();
+  }, [map, position]);
+
+  return container ? createPortal(children, container) : null;
+};
+
+export default MapControl;