feat: implement merchant dashboard, secure auth, and short_id system

- Added dedicated merchant dashboard with analytics and transactions
- Implemented API Key based authentication for merchants
- Introduced 8-character Short IDs for merchants to use in URLs
- Refactored checkout and payment intent APIs to support multi-gateway
- Enhanced Landing Page with Merchant Portal access and marketing copy
- Fixed Next.js 15 async params build issues
- Updated internal branding to P2CGateway
- Added AyrisTech credits to footer

app/not-found.tsx

@@ -0,0 +1,43 @@
+import Link from 'next/link';
+import { ArrowLeft, Search } from 'lucide-react';
+
+export default function NotFound() {
+    return (
+        <div className="min-h-screen bg-[#F8FAFC] flex flex-col items-center justify-center p-6 text-center">
+            <div className="w-24 h-24 bg-blue-100 rounded-[32px] flex items-center justify-center text-blue-600 mb-8 animate-bounce">
+                <Search size={40} />
+            </div>
+
+            <h1 className="text-9xl font-black text-gray-200 leading-none">404</h1>
+            <div className="-mt-12 bg-white px-8 py-2 rounded-2xl shadow-sm border border-gray-100">
+                <h2 className="text-2xl font-black text-gray-900">Sayfa Bulunamadı</h2>
+            </div>
+
+            <p className="text-gray-400 font-bold uppercase tracking-widest text-[10px] mt-8 max-w-xs leading-relaxed">
+                Aradığınız sayfa taşınmış veya silinmiş olabilir. Kaybolmuş hissetmeyin, sizi ana sayfaya götürelim.
+            </p>
+
+            <div className="flex flex-col sm:flex-row gap-4 mt-12 w-full max-w-sm">
+                <Link
+                    href="/"
+                    className="flex-1 px-8 py-4 bg-gray-900 text-white rounded-2xl font-black text-xs uppercase tracking-widest hover:bg-black transition shadow-xl"
+                >
+                    Ana Sayfaya Dön
+                </Link>
+                <Link
+                    href="/admin"
+                    className="flex-1 px-8 py-4 bg-white text-gray-900 border border-gray-100 rounded-2xl font-black text-xs uppercase tracking-widest hover:bg-gray-50 transition"
+                >
+                    Panele Git
+                </Link>
+            </div>
+
+            <div className="mt-20">
+                <div className="inline-flex items-center gap-2 px-4 py-2 bg-blue-50 rounded-full text-blue-600 text-[10px] font-black uppercase tracking-widest border border-blue-100">
+                    <div className="w-1.5 h-1.5 bg-blue-600 rounded-full animate-pulse"></div>
+                    P2CGateway Sistemleri Aktif
+                </div>
+            </div>
+        </div>
+    );
+}