Show waypoint photos from newer p4n2gpx exports

A newer p4n2gpx run (Ruby rewrite, ~/test/mapping/p4n2gpx) started
emitting one plain GPX <link href> per park4night listing photo,
which this app parsed but never displayed. Gpx.waypoint_photos
collects them into a photos property; the waypoint popup renders them
as a row of thumbnails above the description, each opening full-size
in a new tab. Absent on older exports and plain GPS waypoints, so the
row just doesn't render for those.

test/test_gpx.rb

@@ -74,6 +74,18 @@ class GpxTest < Minitest::Test
     assert_nil plain["properties"]["icon"]
   end
 
+  def test_waypoint_captures_link_hrefs_as_photos
+    geojson = Maptool::Gpx.to_geojson(fixture_path("sample_poi.gpx"))
+    with_photos = geojson["features"].find { |f| f["properties"]["name"] == "With photos" }
+    plain = geojson["features"].find { |f| f["properties"]["name"] == "Plain waypoint" }
+
+    assert_equal(
+      ["https://cdn3.park4night.com/lieu/1_100/1_gd.jpg", "https://cdn3.park4night.com/lieu/1_100/2_gd.jpg"],
+      with_photos["properties"]["photos"]
+    )
+    assert_empty plain["properties"]["photos"]
+  end
+
   def test_kinds_detects_routes
     assert_equal ["route"], Maptool::Gpx.kinds(fixture_path("sample_route.gpx"))
   end