feat: add dark mode

app/login/page.tsx

@@ -7,6 +7,7 @@ import { useToast } from "@/components/toast";
 import { ApiError } from "@/lib/api";
 import { Button, Field, Input } from "@/components/ui";
 import { Logo } from "@/components/Logo";
+import { ThemeToggle } from "@/components/ThemeToggle";
 
 export default function LoginPage() {
   const { login, token, ready } = useAuth();
@@ -39,7 +40,10 @@ export default function LoginPage() {
   }
 
   return (
-    <div className="flex min-h-screen items-center justify-center bg-gradient-to-bl from-[#eef1fb] to-[#f6f3fb] p-4">
+    <div className="relative flex min-h-screen items-center justify-center bg-gradient-to-bl from-[#eef1fb] to-[#f6f3fb] p-4 dark:from-[#11151f] dark:to-[#0d1018]">
+      <div className="absolute top-4 left-4">
+        <ThemeToggle />
+      </div>
       <div className="w-full max-w-md rounded-3xl border border-border bg-surface p-8 shadow-lg">
         <div className="mb-8 text-center">
           <div className="mx-auto mb-4 flex h-20 w-20 items-center justify-center rounded-2xl bg-primary-soft">