webui: prevent status bar from being obscured by background

Moved the background from body to .app-main so it stays within safe areas and the status bar remains visible.

webui/src/app.css

@@ -33,7 +33,6 @@ body {
   padding-top: var(--window-inset-top, 0px);
   padding-bottom: var(--window-inset-bottom, 0px);
   margin: 0;
-  background: var(--nord0);
   color: var(--nord6);
   font-family:
     -apple-system, BlinkMacSystemFont, "SF Pro Text", Inter, "Segoe UI", Arial, sans-serif;
@@ -45,6 +44,10 @@ body {
   height: calc(100vh - var(--window-inset-top, 0px) - var(--window-inset-bottom, 0px));
 }
 
+.app-main {
+  background: var(--nord0);
+}
+
 /* Top bar for language selector */
 .top-bar {
   height: 44px;