Holiday switch in the debug menu; darker wood for the treasury chests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lang/nl.lang

@@ -389,6 +389,10 @@ set.debug_ping = Ping tonen
 set.debug_trigger_zones = Triggerzones tonen
 set.debug_command_markers = Debug-commandomarkeringen tonen
 set.debug_path_lines = Padlijnen tonen
+set.debug_holiday = Feestdag
+val.halloween = Halloween
+val.christmas = Kerstmis
+val.easter = Pasen
 
 hint.pickup_prisoner_where = Gevangenen kun je alleen op je eigen gebied oppakken.
 hint.punch_where = De hand kan helden alleen op je eigen gebied slaan.