Fix registration: use bcrypt directly and show real API error messages.

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

frontend/src/pages/LoginPage.tsx

@@ -1,8 +1,18 @@
 import { LockOutlined, UserOutlined } from '@ant-design/icons'
 import { Button, Card, Form, Input, Tabs, Typography, message } from 'antd'
+import axios from 'axios'
 import { Navigate, useNavigate } from 'react-router-dom'
 import { useAuth } from '../context/AuthContext'
 
+function apiErrorMessage(error: unknown, fallback: string) {
+  if (axios.isAxiosError(error)) {
+    const detail = error.response?.data?.detail
+    if (typeof detail === 'string') return detail
+    if (Array.isArray(detail) && detail[0]?.msg) return detail[0].msg
+  }
+  return fallback
+}
+
 export default function LoginPage() {
   const { user, login, register, loading } = useAuth()
   const navigate = useNavigate()
@@ -16,8 +26,8 @@ export default function LoginPage() {
       await login(values.username, values.password)
       message.success('登录成功')
       navigate('/')
-    } catch {
-      message.error('用户名或密码错误')
+    } catch (error) {
+      message.error(apiErrorMessage(error, '用户名或密码错误'))
     }
   }
 
@@ -30,8 +40,8 @@ export default function LoginPage() {
       await register(values.username, values.password)
       message.success('注册成功')
       navigate('/')
-    } catch {
-      message.error('注册失败，用户名可能已存在')
+    } catch (error) {
+      message.error(apiErrorMessage(error, '注册失败，请稍后重试'))
     }
   }