Add theme setting for current line

tests/reference/baseConfig_novelwriter.conf

@@ -1,5 +1,5 @@
 [Meta]
-timestamp = 2025-06-10 23:18:12
+timestamp = 2025-06-14 17:03:01
 
 [Main]
 font = 
@@ -40,6 +40,7 @@ width = 700
 margin = 40
 tabwidth = 40
 cursorwidth = 1
+linehighlight = False
 focuswidth = 800
 hidefocusfooter = False
 justify = False

tests/test_gui/test_gui_theme.py

@@ -632,7 +632,7 @@ def testGuiTheme_CheckTheme(theme):
             "helptext", "fadedtext", "errortext",
         ],
         "Syntax": [
-            "background", "text", "link", "headertext", "headertag",
+            "background", "text", "line", "link", "headertext", "headertag",
             "emphasis", "dialog", "altdialog", "hidden", "note", "shortcode",
             "keyword", "tag", "value", "optional", "spellcheckline",
             "errorline", "replacetag", "modifier", "texthighlight",