Keep print margins white in dark mode

The dark theme sets color-scheme: dark on the root element; Chrome then
paints the page margins of printed pages dark, even with a white
background. The print view forces the light scheme and a white root
background while printing.

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

src/frontend/print/print-document.css

@@ -450,6 +450,11 @@ span.pd-tb-logo-image {
   .print-view {
     background: #fff !important;
   }
+  /* The dark theme sets color-scheme: dark on the root; Chrome then paints
+     the page margins dark. Printing always uses the light scheme. */
+  html:has(.print-view) {
+    color-scheme: light !important;
+  }
   .pd-toolbar,
   .pd-sheet-footer {
     display: none !important;