chore: migrate middleware to proxy as per Next.js 2026 convention

proxy.ts

@@ -0,0 +1,27 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { decrypt } from '@/app/lib/auth';
+
+export async function proxy(request: NextRequest) {
+  const session = request.cookies.get('session')?.value;
+  const { pathname } = request.nextUrl;
+
+  // Protect admin routes
+  if (pathname.startsWith('/admin')) {
+    if (!session) {
+      return NextResponse.redirect(new URL('/login', request.url));
+    }
+
+    try {
+      await decrypt(session);
+      return NextResponse.next();
+    } catch (e) {
+      return NextResponse.redirect(new URL('/login', request.url));
+    }
+  }
+
+  return NextResponse.next();
+}
+
+export const config = {
+  matcher: ['/admin/:path*'],
+};