feat(rover): "only use known ideal locations" toggle

Adds a checkbox in the rover sidebar that constrains the suggested
candidate spots to lat/lon points tagged as :ideal in /rover-locations.
When enabled, Compute.run replaces grid cells with synthetic cells at
each ideal location's exact coordinates, inheriting the propagation
score from the nearest grid cell so atmospheric forecast still factors
in. Path-clearance, terrain, building, and canopy penalties run
unchanged on those snapped candidates.

lib/microwaveprop/rover/compute.ex

@@ -131,8 +131,17 @@ defmodule Microwaveprop.Rover.Compute do
     step.("Loading propagation grid")
     raw_cells = time_step("scores_at", fn -> scores_at.(band_mhz, valid_time, bbox) end)
 
+    ideal_locations = Map.get(args, :ideal_locations, nil)
+
+    candidate_cells =
+      case ideal_locations do
+        nil -> raw_cells
+        [] -> raw_cells
+        locations -> snap_cells_to_locations(locations, raw_cells)
+      end
+
     in_radius =
-      Enum.filter(raw_cells, fn cell ->
+      Enum.filter(candidate_cells, fn cell ->
         DriveTime.haversine_km({home.lat, home.lon}, {cell.lat, cell.lon}) <= radius_km
       end)
 
@@ -325,6 +334,27 @@ defmodule Microwaveprop.Rover.Compute do
     |> Canopy.lookup_many()
   end
 
+  # When the user constrains candidates to known ideal locations, build
+  # synthetic cells at each location's exact lat/lon, inheriting the
+  # propagation score from the nearest grid cell (so atmospheric forecast
+  # still factors in even though the spot itself isn't a grid centroid).
+  defp snap_cells_to_locations(locations, raw_cells) do
+    Enum.flat_map(locations, fn loc ->
+      case nearest_grid_cell(raw_cells, loc) do
+        nil -> []
+        cell -> [%{lat: loc.lat, lon: loc.lon, score: cell.score}]
+      end
+    end)
+  end
+
+  defp nearest_grid_cell([], _loc), do: nil
+
+  defp nearest_grid_cell(cells, loc) do
+    Enum.min_by(cells, fn c ->
+      DriveTime.haversine_km({c.lat, c.lon}, {loc.lat, loc.lon})
+    end)
+  end
+
   defp terrain_db(nil), do: 0.0
 
   defp terrain_db(clearance_m) do

lib/microwaveprop_web/live/rover_live.ex

@@ -67,6 +67,7 @@ defmodule MicrowavepropWeb.RoverLive do
        home_form_error: nil,
        scoring_loading: false,
        scoring_step: nil,
+       only_ideal_locations: false,
        url_loaded?: false
      )}
   end
@@ -193,6 +194,10 @@ defmodule MicrowavepropWeb.RoverLive do
      |> push_event("update_drive_radius", %{km: radius_km})}
   end
 
+  def handle_event("toggle_only_ideal", _params, socket) do
+    {:noreply, assign(socket, only_ideal_locations: not socket.assigns.only_ideal_locations)}
+  end
+
   def handle_event("toggle_station", %{"id" => id}, socket) do
     handle_station_mutation(socket, id, &toggle_station/2)
   end
@@ -713,7 +718,7 @@ defmodule MicrowavepropWeb.RoverLive do
   end
 
   defp scoring_args(socket) do
-    %{
+    base = %{
       home: socket.assigns.home,
       stations: stations_for_compute(socket.assigns.fixed_stations),
       band_mhz: socket.assigns.band,
@@ -722,6 +727,17 @@ defmodule MicrowavepropWeb.RoverLive do
       max_distance_km: socket.assigns.drive_radius_km,
       min_elev_gain: 0
     }
+
+    if socket.assigns.only_ideal_locations do
+      ideals =
+        Rover.list_locations()
+        |> Enum.filter(&(&1.status == :ideal))
+        |> Enum.map(fn l -> %{lat: l.lat, lon: l.lon} end)
+
+      Map.put(base, :ideal_locations, ideals)
+    else
+      base
+    end
   end
 
   defp find_candidate(candidates, grid) do
@@ -1163,6 +1179,27 @@ defmodule MicrowavepropWeb.RoverLive do
             </div>
           </.sidebar_section>
 
+          <.sidebar_section title="CANDIDATES">
+            <label class="flex items-start gap-2 cursor-pointer">
+              <input
+                type="checkbox"
+                checked={@only_ideal_locations}
+                phx-click="toggle_only_ideal"
+                class="checkbox checkbox-sm checkbox-primary mt-0.5"
+              />
+              <span class="text-xs leading-tight">
+                Only use known ideal locations
+                <span class="block text-[10px] opacity-60 mt-0.5">
+                  Restricts suggestions to spots tagged "ideal" in <a
+                    href={~p"/rover-locations"}
+                    class="link"
+                    target="_blank"
+                  >/rover-locations</a>.
+                </span>
+              </span>
+            </label>
+          </.sidebar_section>
+
           <div class="mt-auto p-3 text-[11px] text-neutral-content/50 border-t border-base-300/50">
             Tip: click any cell to see per-station predicted SNR.
           </div>