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/SubsUnion/SubsUnion.js

@@ -12,7 +12,8 @@ const subsUnion = (union, options) => {
   const interactive = options.interactive || false;
 
   if (options.subs) {
-    const lmap = options.map.leafletElement;
+    // v4: options.map is the Leaflet map instance directly (no .leafletElement)
+    const lmap = options.map;
     if (union) {
       lmap.removeLayer(union);
     }
@@ -30,7 +31,7 @@ const subsUnion = (union, options) => {
         if (options.fit && options.bounds) {
           // console.log(options.bounds);
           const bounds = JSON.parse(options.bounds);
-          options.map.leafletElement.fitBounds(L.latLngBounds(bounds._northEast, bounds._southWest));
+          lmap.fitBounds(L.latLngBounds(bounds._northEast, bounds._southWest));
         }
       } else if (options.subs.length > 0) {
         const result = calcUnion(L, options.subs, sub => sub, true);
@@ -43,7 +44,7 @@ const subsUnion = (union, options) => {
         });
         union.addTo(lmap);
         if (options.fit) {
-          options.map.leafletElement.fitBounds(bounds);
+          lmap.fitBounds(bounds);
         }
       }
     }