Make Sortiment a button

Converted Sortiment link in header to a bordered button style to match Abonnemang, using a brown-red outline and hover effects for visual emphasis.

X-Lovable-Edit-ID: edt-3c3b6e21-f271-4074-8d67-9c9694ede3ec

src/components/Header.tsx

@@ -8,8 +8,8 @@ const Header = () => {
           <Logo size="small" />
         </a>
         
-        <nav className="hidden md:flex items-center gap-6 text-sm">
-          <a href="#gallery" className="text-muted-foreground hover:text-primary transition-colors">
+        <nav className="hidden md:flex items-center gap-4 text-sm">
+          <a href="#gallery" className="border-2 border-primary text-primary px-4 py-2 rounded-sm hover:bg-primary hover:text-primary-foreground transition-colors">
             Sortiment
           </a>
           <a href="#plans" className="bg-primary text-primary-foreground px-4 py-2 rounded-sm hover:bg-primary/90 transition-colors">