Adjust scroll activation threshold and reset inverseYPos.

Increased the scroll threshold for activating the header to 5 for better usability. Added a reset for `inverseYPos` to 0 when the scroll position is at the top, ensuring consistent behavior.

frontend/src/app/header/header.component.ts

@@ -27,10 +27,11 @@ export class HeaderComponent {
   @HostListener('window:scroll', [])
   onWindowScroll(): void {
     const scrollPosition = window.scrollY;
-    if (scrollPosition > 0) {
+    if (scrollPosition > 5) {
       this.active = 'active';
       this.inverseYPos = scrollPosition - (scrollPosition * 0.2);
     } else {
+      this.inverseYPos = 0;
       this.active = '';
     }
   }