Draw a LiveTrack session's planned course alongside the actual track

Garmin's own LiveTrack page already shows both when the activity was
started from a saved course — the session payload carries the course's
geoPoints right alongside the track points (LiveTrackClient found it
nested under the same React Query cache the session/points come from).

Rendered as a second, dashed LineString distinct from the actual
track's own line ("kind": "actual" vs "planned" on each GeoJSON
feature) — muted gray rather than matching Garmin's own purple-for-
planned, since this app's actual track is already purple and reusing
it would make the two indistinguishable.

app.rb

@@ -743,24 +743,36 @@ module Maptool
       halt 502, json(error: "track has no positions") if coordinates.empty?
       last = points.last
 
-      json(
-        type: "FeatureCollection",
-        features: [
-          { type: "Feature", geometry: { type: "LineString", coordinates: coordinates }, properties: {} },
-          {
-            type: "Feature",
-            geometry: { type: "Point", coordinates: coordinates.last },
-            # Merges the session summary in too — the point layer's hover
-            # popup (public/js/livetrack.js) reads it straight off here
-            # rather than needing a second fetch against /sessions.
-            properties: summary.merge(
-              "time" => last["dateTime"],
-              "speed_meters_per_sec" => last["speedMetersPerSec"],
-              "heart_rate_beats_per_min" => last["heartRateBeatsPerMin"]
-            ),
-          },
-        ]
-      )
+      features = [
+        { type: "Feature", geometry: { type: "LineString", coordinates: coordinates }, properties: { "kind" => "actual" } },
+        {
+          type: "Feature",
+          geometry: { type: "Point", coordinates: coordinates.last },
+          # Merges the session summary in too — the point layer's hover
+          # popup (public/js/livetrack.js) reads it straight off here
+          # rather than needing a second fetch against /sessions.
+          properties: summary.merge(
+            "time" => last["dateTime"],
+            "speed_meters_per_sec" => last["speedMetersPerSec"],
+            "heart_rate_beats_per_min" => last["heartRateBeatsPerMin"]
+          ),
+        },
+      ]
+
+      # Only present when the activity was started from a saved Garmin
+      # course (see LiveTrackClient#fetch) — plotted separately from the
+      # actual track ("kind" distinguishes the two LineStrings) since it's
+      # the planned route, not where the person has actually been.
+      course_coordinates = result.course&.[]("geoPoints")&.filter_map { |p| p.dig("position", "lon") && p.dig("position", "lat") && [p["position"]["lon"], p["position"]["lat"]] }
+      if course_coordinates&.any?
+        features << {
+          type: "Feature",
+          geometry: { type: "LineString", coordinates: course_coordinates },
+          properties: { "kind" => "planned", "name" => result.course["name"] },
+        }
+      end
+
+      json(type: "FeatureCollection", features: features)
     end
 
     get "/api/gnss/position" do