feat(rover): Maidenhead grid overlay on location detail map

LocationMap hook now adds a togglable grid layer (matching the contact
map pattern) so the rover-location detail page shows the standard
Maidenhead overlay alongside the marker.

assets/js/location_map_hook.ts

@@ -1,8 +1,11 @@
 import type { ViewHook } from "phoenix_live_view"
+import { updateGridOverlay } from "./maidenhead_grid"
 
 interface LocationMapHook extends ViewHook {
   map: L.Map
   marker: L.CircleMarker
+  gridLayer: L.LayerGroup
+  gridVisible: boolean
   visibilityHandler: (() => void) | null
 }
 
@@ -48,6 +51,39 @@ export const LocationMap: Partial<LocationMapHook> = {
     }).addTo(map)
     this.marker.bindPopup(`${lat.toFixed(6)}, ${lon.toFixed(6)}`)
 
+    // Maidenhead grid overlay + toggle
+    this.gridLayer = L.layerGroup().addTo(map)
+    this.gridVisible = true
+    updateGridOverlay(map, this.gridLayer)
+    map.on("moveend", () => {
+      if (this.gridVisible) updateGridOverlay(map, this.gridLayer)
+    })
+
+    const GridToggle = L.Control.extend({
+      options: { position: "topright" as const },
+      onAdd: () => {
+        const btn = L.DomUtil.create("button", "leaflet-bar leaflet-control")
+        btn.innerHTML = "Grid"
+        btn.title = "Toggle Maidenhead grid"
+        btn.style.cssText =
+          "background:#fff;padding:4px 8px;font-size:12px;cursor:pointer;font-weight:600;"
+        L.DomEvent.disableClickPropagation(btn)
+        btn.onclick = () => {
+          this.gridVisible = !this.gridVisible
+          if (this.gridVisible) {
+            this.gridLayer.addTo(map)
+            updateGridOverlay(map, this.gridLayer)
+            btn.style.opacity = "1"
+          } else {
+            this.gridLayer.remove()
+            btn.style.opacity = "0.5"
+          }
+        }
+        return btn
+      }
+    })
+    new GridToggle().addTo(map)
+
     // LiveView reconnect / tab visibility — Leaflet needs invalidateSize.
     this.visibilityHandler = () => {
       if (document.visibilityState === "visible") this.map.invalidateSize()