Update favicon and enhance SiteHeader component with logo image for improved branding

src/components/site-header.tsx

@@ -1,5 +1,5 @@
+import Image from "next/image";
 import Link from "next/link";
-import { GraduationCap } from "lucide-react";
 import { UserNav } from "@/components/user-nav";
 
 const navLinks = [
@@ -14,8 +14,16 @@ export function SiteHeader() {
       <div className="mx-auto flex h-16 max-w-6xl items-center justify-between gap-3 px-4">
         <Link
           href="/"
-          className="group flex items-center gap-3 font-bricolage text-xl"
+          className="group flex items-center font-bricolage text-xl"
         >
+          <Image
+            src="/kolay-tercih-mark.svg"
+            alt=""
+            width={44}
+            height={44}
+            aria-hidden="true"
+            className="size-11 shrink-0"
+          />
           <span>
             <span className="font-light text-3xl tracking-tighter">Kolay</span>
             <span className="font-semibold text-3xl tracking-tighter">