improve contrast of muted text in light mode

src/app.css

@@ -35,7 +35,7 @@ body {
   /* Web layout - 5 colors using light-dark() for dark mode */
   --color-bg: light-dark(#fafafa, #0c0c0e);
   --color-fg: light-dark(#18181b, #fafafa);
-  --color-muted: light-dark(#71717a, #a1a1aa);
+  --color-muted: light-dark(#56565d, #a1a1aa);
   --color-accent: light-dark(#0e7490, #22d3ee);
   --color-hot: light-dark(#c2410c, #fb923c);