refactor(layout, i18n, admin): 优化布局结构与多语言支持

调整 AdminShell 组件的子组件顺序，提升代码可读性。更新 admin-breadcrumb 组件，简化导航标签翻译逻辑，确保多语言支持的一致性。重构 admin-language-switcher 组件，优化语言切换的用户体验，增强界面交互性。更新多语言配置，新增登录界面的副标题，提升用户体验。

src/components/admin/auth-gate.tsx

@@ -2,40 +2,86 @@
 
 import { useRouter } from "next/navigation";
 import { useEffect, useState, type ReactNode } from "react";
-import { useTranslation } from "react-i18next";
 
+import { AdminAuthCheckingScreen } from "@/components/admin/admin-auth-checking";
+import { verifyStoredAdminSession } from "@/lib/admin-session-verify";
+import { useAdminSessionStore } from "@/stores/admin-session";
 import { readToken } from "@/stores/admin-token";
 
 type ShellAuthGateProps = {
   children: ReactNode;
 };
 
+type GateStatus = "pending" | "authed" | "guest";
+
+function hasAdminToken(bearerToken: string | null): boolean {
+  const token = bearerToken ?? readToken();
+  return token != null && token.trim() !== "";
+}
+
 /**
- * Shell route guard. Reads the auth token from localStorage on the client and
- * redirects to the login page when no token is present.
+ * Shell 路由守卫：无 Token 或 `/auth/me` 校验失败时跳转登录页。
  */
 export function ShellAuthGate({ children }: ShellAuthGateProps) {
-  const { t } = useTranslation("common");
   const router = useRouter();
-  const [allowed, setAllowed] = useState(false);
+  const bearerToken = useAdminSessionStore((s) => s.bearerToken);
+  const [status, setStatus] = useState<GateStatus>("pending");
+
+  const setShellAuthPending = useAdminSessionStore((s) => s.setShellAuthPending);
 
   useEffect(() => {
-    const token = readToken();
-    if (!token) {
-      router.replace("/admin/login");
-      return;
-    }
-    queueMicrotask(() => {
-      setAllowed(true);
-    });
-  }, [router]);
+    let cancelled = false;
+    setShellAuthPending(true);
 
-  if (!allowed) {
-    return (
-      <div className="flex min-h-[50vh] w-full flex-1 items-center justify-center text-sm text-muted-foreground">
-        {t("auth.checking", { defaultValue: "Checking sign-in status…" })}
-      </div>
-    );
+    async function run() {
+      if (!hasAdminToken(bearerToken)) {
+        if (!cancelled) {
+          setStatus("guest");
+        }
+        return;
+      }
+
+      if (!cancelled) {
+        setStatus("pending");
+      }
+
+      const ok = await verifyStoredAdminSession();
+      if (cancelled) {
+        return;
+      }
+
+      if (ok) {
+        setStatus("authed");
+        return;
+      }
+
+      setStatus("guest");
+    }
+
+    void run().finally(() => {
+      if (!cancelled) {
+        setShellAuthPending(false);
+      }
+    });
+
+    return () => {
+      cancelled = true;
+      setShellAuthPending(false);
+    };
+  }, [bearerToken, setShellAuthPending]);
+
+  useEffect(() => {
+    if (status === "guest") {
+      router.replace("/admin/login");
+    }
+  }, [status, router]);
+
+  if (status === "pending") {
+    return <AdminAuthCheckingScreen variant="shell" />;
+  }
+
+  if (status === "guest") {
+    return null;
   }
 
   return children;