frontend: redesign homepage with magic dock and login dialog

- Replace top login/register buttons with magic dock navigation
- Add dock items: home, downloads, blog, and conditional login/logout
- Show dashboard icon in dock when authenticated
- Extract HomePageClient for client-side dialog state

frontend/app/login-dialog.tsx

@@ -0,0 +1,38 @@
+"use client";
+
+import {
+  Dialog,
+  DialogContent,
+  DialogHeader,
+  DialogTitle,
+  DialogTrigger,
+} from "@/components/ui/dialog";
+import { LoginForm } from "./login/login-form";
+import { ReactNode, useState } from "react";
+
+export function LoginDialog({
+  hasKeycloak,
+  children,
+}: {
+  hasKeycloak: boolean;
+  children?: ReactNode;
+}) {
+  const [open, setOpen] = useState(false);
+
+  return (
+    <Dialog open={open} onOpenChange={setOpen}>
+      <DialogTrigger className="rounded-lg bg-slate-900 px-5 py-2.5 text-sm font-medium text-white hover:bg-slate-800">
+        {children ?? "登录"}
+      </DialogTrigger>
+      <DialogContent className="sm:max-w-md">
+        <DialogHeader>
+          <DialogTitle className="text-center">登录</DialogTitle>
+        </DialogHeader>
+        <LoginForm
+          hasKeycloak={hasKeycloak}
+          onSuccess={() => setOpen(false)}
+        />
+      </DialogContent>
+    </Dialog>
+  );
+}