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

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

src/main.rs

@@ -480,6 +480,7 @@ fn apply_settings(s: &Settings, r3d: &mut R3d) {
     r3d.set_wall_detail(s.wall_subdivisions());
     r3d.max_lights = s.max_lights as usize;
     r3d.pixel_rows = settings::pixel_rows(s.pixel_rows);
+    holiday::set_override(s.debug_holiday);
     audio::set_volumes(s.music_volume, s.volume, s.muted);
 }