feat: add Keycloak authentication

src/app/auth-startup-screen.tsx

@@ -0,0 +1,26 @@
+import { Droplets, RefreshCw } from "lucide-react";
+import { Button } from "@/shared/ui/button";
+
+export function AuthStartupScreen({ error }: { error?: boolean }) {
+  return (
+    <main className="grid min-h-[100dvh] place-items-center bg-slate-100 px-5 text-slate-900">
+      <section className="surface-reading w-full max-w-md p-6 text-center shadow-xl shadow-slate-900/5">
+        <span className="mx-auto grid h-11 w-11 place-items-center rounded-xl bg-blue-600 text-white">
+          <Droplets size={22} aria-hidden="true" />
+        </span>
+        <h1 className="mt-4 text-lg font-semibold">
+          {error ? "统一身份认证连接失败" : "正在连接统一身份认证"}
+        </h1>
+        <p className="mt-2 text-sm leading-6 text-slate-500">
+          {error ? "请检查网络或 Keycloak 配置后重试。" : "正在检查登录状态，请稍候。"}
+        </p>
+        {error ? (
+          <Button className="mt-5" onClick={() => window.location.reload()}>
+            <RefreshCw size={15} aria-hidden="true" />
+            重新连接
+          </Button>
+        ) : null}
+      </section>
+    </main>
+  );
+}