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/GoogleMutantLayer.js

@@ -0,0 +1,25 @@
+import { createLayerComponent } from '@react-leaflet/core';
+import L from 'leaflet';
+import 'leaflet.gridlayer.googlemutant';
+
+// Replacement for react-leaflet-google's GoogleLayer (v1-only). The Google Maps
+// JS API is already loaded (with the places library) by Gkeys before any Google
+// BaseLayer renders, so googlemutant can use window.google.maps directly.
+function createGoogleMutant({
+  maptype = 'roadmap', opacity, googlekey, ...options
+}, ctx) {
+  const instance = L.gridLayer.googleMutant({
+    type: String(maptype).toLowerCase(),
+    ...(opacity != null ? { opacity } : {}),
+    ...options
+  });
+  return { instance, context: { ...ctx } };
+}
+
+function updateGoogleMutant(instance, props, prevProps) {
+  if (props.opacity != null && props.opacity !== prevProps.opacity) {
+    instance.setOpacity(props.opacity);
+  }
+}
+
+export default createLayerComponent(createGoogleMutant, updateGoogleMutant);