fix(css): Handle system auto-light mode for headerlink colors

The light mode override for headerlink colors used body:not([data-theme="dark"])
which incorrectly matches auto mode even when system is dark. Split into
explicit light selector plus media query for auto + system light.

Author: tony

docs/_static/css/argparse-highlight.css

@@ -333,15 +333,26 @@ pre.argparse-usage {
 
 /*
  * Light mode headerlink color overrides
+ * Needed because code block has dark background regardless of theme
  */
-body:not([data-theme="dark"]) .argparse-argument-name .headerlink {
+body[data-theme="light"] .argparse-argument-name .headerlink {
 	color: #9ca0a5;
 
 	&:hover:not(:visited) {
 		color: #cfd0d0;
 	}
 }
 
+@media (prefers-color-scheme: light) {
+	body:not([data-theme="dark"]) .argparse-argument-name .headerlink {
+		color: #9ca0a5;
+
+		&:hover:not(:visited) {
+			color: #cfd0d0;
+		}
+	}
+}
+
 /*
  * Highlight when targeted via URL fragment
  * Uses Furo's highlight-on-target color for consistency.