feat: implement configuration management and enhance user registration flow

k-tv-frontend/app/(auth)/register/page.tsx

@@ -3,11 +3,27 @@
 import Link from "next/link";
 import { useState } from "react";
 import { useRegister } from "@/hooks/use-auth";
+import { useConfig } from "@/hooks/use-channels";
 
 export default function RegisterPage() {
   const [email, setEmail] = useState("");
   const [password, setPassword] = useState("");
   const { mutate: register, isPending, error } = useRegister();
+  const { data: config } = useConfig();
+
+  if (config && !config.allow_registration) {
+    return (
+      <div className="w-full max-w-sm space-y-4 text-center">
+        <h1 className="text-xl font-semibold text-zinc-100">Registration disabled</h1>
+        <p className="text-sm text-zinc-500">
+          The administrator has disabled new account registration.
+        </p>
+        <Link href="/login" className="inline-block text-sm text-zinc-300 hover:text-white">
+          Sign in instead
+        </Link>
+      </div>
+    );
+  }
 
   const handleSubmit = (e: React.FormEvent) => {
     e.preventDefault();