style(sidebar): set light-mode sidenav background to white; keep dark mode background via variable

Author: codyde

src/components/sidebar/style.module.scss

@@ -2,12 +2,15 @@
   .sidebar.sidebar {
     --sidebar-item-bg-hover: var(--gray-a4);
     --sidebar-item-color: var(--accent);
+    /* Keep a darker background in dark mode */
+    background-color: var(--gray-1);
   }
 }
 .sidebar {
   --sidebar-item-bg-hover: var(--accent-purple-light);
   --sidebar-item-color: var(--accent-purple);
-  background-color: var(--gray-1);
+  /* Light mode: use pure white background */
+  background-color: #ffffff;
   top: var(--header-height);
   bottom: 0;
   flex-direction: column;