feat(hierarchy): name the route a native tree shows

The screen name was web-only: the Chrome driver stamps sanderling-screen on
the root and nothing else does, so every Android and iOS step recorded and
logged an empty screen. The route marker the tree already carries (the
resource id ending in Screen, the same one Transitional counts) names it.

internal/hierarchy/hierarchy_test.go

@@ -1821,3 +1821,57 @@ func TestTagMatchesTheElementItNames(t *testing.T) {
 		})
 	}
 }
+
+func TestScreenNameNamesTheRouteTheTreeShows(t *testing.T) {
+	cases := []struct {
+		name string
+		tree string
+		want string
+	}{
+		{
+			"driver-set screen",
+			`{"attributes": {"bounds": "[0,0,10,10]", "sanderling-screen": "/ledger"}, "children": []}`,
+			"/ledger",
+		},
+		{
+			"route marker",
+			`{"attributes": {"bounds": "[0,0,10,10]"}, "children": [
+				{"attributes": {"resource-id": "HomeScreen", "bounds": "[0,0,10,10]"}, "children": []}
+			]}`,
+			"HomeScreen",
+		},
+		{
+			"route marker repeated by a nested node",
+			`{"attributes": {"bounds": "[0,0,10,10]"}, "children": [
+				{"attributes": {"resource-id": "HomeScreen", "bounds": "[0,0,10,10]"}, "children": [
+					{"attributes": {"resource-id": "HomeScreen", "bounds": "[0,0,10,5]"}, "children": []}
+				]}
+			]}`,
+			"HomeScreen",
+		},
+		{
+			"cross-fade names no screen",
+			`{"attributes": {"bounds": "[0,0,10,10]"}, "children": [
+				{"attributes": {"resource-id": "HomeScreen", "bounds": "[0,0,10,10]"}, "children": []},
+				{"attributes": {"resource-id": "LedgerScreen", "bounds": "[0,0,10,10]"}, "children": []}
+			]}`,
+			"",
+		},
+		{
+			"no marker at all",
+			`{"attributes": {"bounds": "[0,0,10,10]"}, "children": []}`,
+			"",
+		},
+	}
+	for _, testCase := range cases {
+		t.Run(testCase.name, func(t *testing.T) {
+			tree, err := Parse(testCase.tree)
+			if err != nil {
+				t.Fatalf("Parse: %v", err)
+			}
+			if got := tree.ScreenName(); got != testCase.want {
+				t.Errorf("ScreenName = %q, want %q", got, testCase.want)
+			}
+		})
+	}
+}