Added a thin blue line using a separate header-line.css file

Maintained the existing header gradient and all other functionality
No modifications to existing variables or hover effects

public/components/header.html

@@ -20,6 +20,7 @@
             <i class="fas fa-bars"></i>
         </button>
     </div>
+    <div class="header-horizontal-line"></div>
     <script>
         // Hide expertise and contact links on non-index pages
         if (window.location.pathname !== '/' && window.location.pathname !== '/index.html') {