feat(rover): show buildings stacked on terrain in path profile

Each profile sample now carries the tallest building height within 80m
of the path point. The candidate-detail SVG renders these as a red
polygon stacked on top of the terrain so blockage from buildings is
visible alongside ridges. max_obstacle_m now reflects building tops too,
so the clearance label downgrades when buildings sit on the link.

lib/microwaveprop/rover/candidate_detail.ex

@@ -5,6 +5,7 @@ defmodule Microwaveprop.Rover.CandidateDetail do
   along the great-circle path to each selected fixed station.
   """
 
+  alias Microwaveprop.Buildings.Index, as: BuildingsIndex
   alias Microwaveprop.Radio.Maidenhead
   alias Microwaveprop.Rover.DriveTime
   alias Microwaveprop.Rover.LinkMargin
@@ -12,6 +13,11 @@ defmodule Microwaveprop.Rover.CandidateDetail do
 
   @sample_count 48
 
+  # Search radius around each profile sample when checking buildings.
+  # Slightly tighter than the path-clearance radius (150 m) because the
+  # profile is a narrower visualization — we want what's "on the line".
+  @profile_building_radius_m 80
+
   @type station :: %{callsign: String.t(), lat: float(), lon: float()}
 
   @type link_summary :: %{
@@ -24,7 +30,7 @@ defmodule Microwaveprop.Rover.CandidateDetail do
           station_elev_m: integer() | nil,
           max_obstacle_m: integer() | nil,
           clearance_m: integer() | nil,
-          profile: [%{dist_km: float(), elev: integer()}]
+          profile: [%{dist_km: float(), elev: integer(), building_m: float()}]
         }
 
   @spec summarize(map(), [station()], non_neg_integer(), DateTime.t(), atom()) :: %{
@@ -43,7 +49,7 @@ defmodule Microwaveprop.Rover.CandidateDetail do
         max_obstacle =
           profile
           |> middle_samples()
-          |> Enum.map(& &1.elev)
+          |> Enum.map(fn pt -> pt.elev + round(pt.building_m) end)
           |> safe_max()
 
         clearance =
@@ -93,7 +99,13 @@ defmodule Microwaveprop.Rover.CandidateDetail do
            @sample_count
          ) do
       {:ok, points} ->
-        Enum.map(points, fn pt -> %{dist_km: pt.dist_km, elev: pt.elev} end)
+        Enum.map(points, fn pt ->
+          %{
+            dist_km: pt.dist_km,
+            elev: pt.elev,
+            building_m: BuildingsIndex.max_height_near(pt.lat, pt.lon, @profile_building_radius_m)
+          }
+        end)
 
       _ ->
         []

lib/microwaveprop_web/live/rover_live.ex

@@ -791,9 +791,10 @@ defmodule MicrowavepropWeb.RoverLive do
   defp profile_to_svg([]), do: nil
 
   defp profile_to_svg(points) do
+    tops = Enum.map(points, fn pt -> pt.elev + round(Map.get(pt, :building_m, 0.0)) end)
     elevs = Enum.map(points, & &1.elev)
     min_e = Enum.min(elevs)
-    max_e = Enum.max(elevs)
+    max_e = max(Enum.max(elevs), Enum.max(tops))
     span = max(max_e - min_e, 1)
     first = List.first(points)
     last = List.last(points)
@@ -808,12 +809,38 @@ defmodule MicrowavepropWeb.RoverLive do
 
     fill = "0,60 " <> line <> " 240,60"
 
+    has_buildings? = Enum.any?(points, fn pt -> Map.get(pt, :building_m, 0.0) > 0.5 end)
+
+    building_fill =
+      if has_buildings? do
+        building_line =
+          Enum.map_join(points, " ", fn pt ->
+            x = pt.dist_km / total_km * 240.0
+            top = pt.elev + round(Map.get(pt, :building_m, 0.0))
+            y = 60.0 - (top - min_e) / span * 50.0
+            "#{Float.round(x, 2)},#{Float.round(y, 2)}"
+          end)
+
+        # Close back along the terrain so the building polygon sits on top.
+        terrain_back =
+          points
+          |> Enum.reverse()
+          |> Enum.map_join(" ", fn pt ->
+            x = pt.dist_km / total_km * 240.0
+            y = 60.0 - (pt.elev - min_e) / span * 50.0
+            "#{Float.round(x, 2)},#{Float.round(y, 2)}"
+          end)
+
+        building_line <> " " <> terrain_back
+      end
+
     los_y_start = Float.round(60.0 - (first.elev - min_e) / span * 50.0, 2)
     los_y_end = Float.round(60.0 - (last.elev - min_e) / span * 50.0, 2)
 
     %{
       line: line,
       fill: fill,
+      building_fill: building_fill,
       start_elev_m: first.elev,
       end_elev_m: last.elev,
       total_km: total_km,
@@ -1208,6 +1235,13 @@ defmodule MicrowavepropWeb.RoverLive do
     ~H"""
     <svg viewBox="0 0 240 64" class="w-full h-12 mt-1" preserveAspectRatio="none">
       <polygon points={@svg.fill} fill="rgb(14 165 233 / 0.25)" />
+      <polygon
+        :if={@svg.building_fill}
+        points={@svg.building_fill}
+        fill="rgb(220 38 38 / 0.55)"
+        stroke="#dc2626"
+        stroke-width="0.6"
+      />
       <polyline points={@svg.line} fill="none" stroke="#0ea5e9" stroke-width="1.2" />
       <line
         x1="0"