fix(style): improve hero tagline contrast

Targets the Starlight hero tagline element to use the primary colour variable, ensuring readable contrast in both light and dark modes.

src/styles/style.css

@@ -146,6 +146,10 @@ starlight-theme-select > label {
   background-color: var(--witch-plum) !important;
 }
 
+.hero .tagline {
+  color: var(--primary-color) !important;
+}
+
 #extra-footer-content {
   display: flex;
   flex-direction: row;