Add login gate, calculation history, and AI markdown download.

Co-authored-by: Cursor <cursoragent@cursor.com>

components/auth/login-form.tsx

@@ -0,0 +1,76 @@
+"use client";
+
+import { useState } from "react";
+import { useRouter, useSearchParams } from "next/navigation";
+import { Button } from "@/components/ui/button";
+import { useAuth } from "@/components/auth/auth-provider";
+
+export default function LoginForm() {
+  const router = useRouter();
+  const searchParams = useSearchParams();
+  const { refresh } = useAuth();
+  const [username, setUsername] = useState("");
+  const [password, setPassword] = useState("");
+  const [error, setError] = useState("");
+  const [loading, setLoading] = useState(false);
+
+  async function handleSubmit(e: React.FormEvent) {
+    e.preventDefault();
+    setError("");
+    setLoading(true);
+    try {
+      const res = await fetch("/api/auth/login", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ username, password }),
+      });
+      const data = await res.json();
+      if (!res.ok) {
+        setError(data.error ?? "登录失败");
+        return;
+      }
+      await refresh();
+      const next = searchParams.get("next") || "/liuyao";
+      router.push(next);
+      router.refresh();
+    } catch {
+      setError("网络错误，请稍后重试");
+    } finally {
+      setLoading(false);
+    }
+  }
+
+  return (
+    <form onSubmit={handleSubmit} className="mx-auto w-full max-w-sm space-y-4">
+      <div className="space-y-2">
+        <label className="text-sm font-medium">用户名</label>
+        <input
+          type="text"
+          autoComplete="username"
+          className="w-full rounded-md border bg-background px-3 py-2 text-sm"
+          value={username}
+          onChange={(e) => setUsername(e.target.value)}
+          required
+        />
+      </div>
+      <div className="space-y-2">
+        <label className="text-sm font-medium">密码</label>
+        <input
+          type="password"
+          autoComplete="current-password"
+          className="w-full rounded-md border bg-background px-3 py-2 text-sm"
+          value={password}
+          onChange={(e) => setPassword(e.target.value)}
+          required
+        />
+      </div>
+      {error && <p className="text-sm text-destructive">{error}</p>}
+      <Button type="submit" className="w-full" disabled={loading}>
+        {loading ? "登录中…" : "登录"}
+      </Button>
+      <p className="text-center text-xs text-muted-foreground">
+        登录后可使用六爻算卦、生辰八字、综合测算与测算历史
+      </p>
+    </form>
+  );
+}