feat: implement sticky header with height compression and glassmorphism

default.hbs

@@ -5,6 +5,7 @@
         mobileMenuOpen: false,
         currentPath: window.location.pathname,
         showScrollTop: false,
+        isSticky: false,
         init() {
             $watch('theme', val => {
                 localStorage.setItem('theme', val);
@@ -13,9 +14,10 @@
             document.documentElement.setAttribute('data-theme', this.theme);
             document.documentElement.classList.remove('hidden');
 
-            // Handle scroll for scroll-to-top button
+            // Handle scroll for sticky header and scroll-to-top button
             window.addEventListener('scroll', () => {
                 this.showScrollTop = window.scrollY > 400;
+                this.isSticky = window.scrollY > 50;
             });
 
             // Update currentPath on navigation to keep menu highlights in sync