refactor(api): convert API functions to async/await with typed returns

Replace raw axios promise returns with async functions that unwrap
response data, providing stronger type guarantees at call sites.

- Unwrap `res.data.data` in all API functions instead of exposing
  AxiosResponse to consumers
- Add missing return types (LoginVo, BorrowInfoVo, Book, etc.)
- Convert all exported functions to async syntax

src/features/auth/LoginPage.tsx

@@ -0,0 +1,120 @@
+import { useState, useEffect, type FormEvent } from "react"
+import { useNavigate, Navigate } from "react-router-dom"
+import { toast } from "sonner"
+import { Loader2Icon } from "lucide-react"
+import { Card, CardHeader, CardTitle, CardContent, CardFooter } from "@/components/ui/card"
+import { Label } from "@/components/ui/label"
+import { Input } from "@/components/ui/input"
+import { Button } from "@/components/ui/button"
+import { useAuthStore } from "@/store/authStore"
+import { login } from "@/api/auth"
+import { setBaseUrl } from "@/api/client"
+
+export default function LoginPage() {
+  const navigate = useNavigate()
+  const token = useAuthStore((s) => s.token)
+  const role = useAuthStore((s) => s.role)
+  const setAuth = useAuthStore((s) => s.setAuth)
+
+  const [serverUrl, setServerUrl] = useState("")
+  const [username, setUsername] = useState("")
+  const [password, setPassword] = useState("")
+  const [errors, setErrors] = useState<Record<string, string>>({})
+  const [loading, setLoading] = useState(false)
+
+  useEffect(() => {
+    setServerUrl(localStorage.getItem("api_base_url") || "")
+  }, [])
+
+  if (token) {
+    return <Navigate to={role === "ADMIN" ? "/admin/books" : "/books"} replace />
+  }
+
+  function validate(): boolean {
+    const next: Record<string, string> = {}
+    if (!serverUrl.trim()) next.serverUrl = "服务器地址不能为空"
+    if (!username.trim()) next.username = "用户名不能为空"
+    if (!password) next.password = "密码不能为空"
+    setErrors(next)
+    return Object.keys(next).length === 0
+  }
+
+  async function handleSubmit(e: FormEvent) {
+    e.preventDefault()
+    if (!validate()) return
+
+    setLoading(true)
+    try {
+      setBaseUrl(serverUrl.trim())
+      const result = await login({ username: username.trim(), password })
+      setAuth(result)
+      toast.success("登录成功")
+      navigate(result.role === "ADMIN" ? "/admin/books" : "/books", { replace: true })
+    } catch (err) {
+      toast.error(err instanceof Error ? err.message : "登录失败")
+    } finally {
+      setLoading(false)
+    }
+  }
+
+  return (
+    <div className="flex min-h-screen items-center justify-center px-4">
+      <Card className="w-full max-w-md">
+        <CardHeader>
+          <CardTitle className="text-center text-xl">图书管理系统</CardTitle>
+        </CardHeader>
+        <form onSubmit={handleSubmit}>
+          <CardContent className="space-y-4">
+            <div className="space-y-2">
+              <Label htmlFor="serverUrl">服务器地址</Label>
+              <Input
+                id="serverUrl"
+                type="url"
+                placeholder="http://localhost:8080"
+                value={serverUrl}
+                onChange={(e) => setServerUrl(e.target.value)}
+                aria-invalid={!!errors.serverUrl}
+              />
+              {errors.serverUrl && (
+                <p className="text-sm text-destructive">{errors.serverUrl}</p>
+              )}
+            </div>
+            <div className="space-y-2">
+              <Label htmlFor="username">用户名</Label>
+              <Input
+                id="username"
+                placeholder="用户名"
+                value={username}
+                onChange={(e) => setUsername(e.target.value)}
+                aria-invalid={!!errors.username}
+              />
+              {errors.username && (
+                <p className="text-sm text-destructive">{errors.username}</p>
+              )}
+            </div>
+            <div className="space-y-2">
+              <Label htmlFor="password">密码</Label>
+              <Input
+                id="password"
+                type="password"
+                placeholder="密码"
+                value={password}
+                onChange={(e) => setPassword(e.target.value)}
+                aria-invalid={!!errors.password}
+              />
+              {errors.password && (
+                <p className="text-sm text-destructive">{errors.password}</p>
+              )}
+            </div>
+          </CardContent>
+          <CardFooter>
+            <Button type="submit" className="w-full" disabled={loading}>
+              {loading && <Loader2Icon className="animate-spin" />}
+              {loading ? "登录中..." : "登录"}
+            </Button>
+          </CardFooter>
+        </form>
+      </Card>
+    </div>
+  )
+}

src/router/index.tsx

@@ -1,10 +1,8 @@
 import { createBrowserRouter, Navigate } from "react-router-dom"
 import { ProtectedRoute, AdminRoute } from "./guards"
+import LoginPage from "@/features/auth/LoginPage"
 
 // Placeholder components — real pages will replace these
-function LoginPage() {
-  return <div>Login</div>
-}
 function BooksPage() {
   return <div>Books</div>
 }