Keep report paper text black in every theme

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

frontend/src/components/ReportEditor/EditorCanvas.css

@@ -13,6 +13,7 @@
   width: 1440px;
   height: 2112px;
   background: white;
+  color: #000;
   border: 1px solid #ccc;
   box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
   font-family: 'Courier New', 'Consolas', monospace;

frontend/src/components/ReportEditor/a4/A4Canvas.css

@@ -13,6 +13,7 @@
 .a4-page {
   position: relative;
   background: #fff;
+  color: #000;
   box-shadow: 0 2px 12px rgba(0, 0, 0, 0.35);
   flex: none;
 }

frontend/src/components/ReportEditor/a4/print/print.css

@@ -36,6 +36,7 @@
   position: relative;
   overflow: hidden;
   background: #fff;
+  color: #000;
   page-break-after: always;
   break-after: page;
 }