fix(wallet-service, admin-web): 修复系统账户划转金额类型问题

- wallet-service: 支持 amount 为字符串或数字类型，添加类型转换
- admin-web: 改进错误处理，正确提取 Axios 错误消息

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/wallet-service/src/api/controllers/system-withdrawal.controller.ts

@@ -28,7 +28,7 @@ import { SystemWithdrawalApplicationService } from '@/application/services';
 class SystemWithdrawalRequestDTO {
   fromAccountSequence: string;
   toAccountSequence: string;
-  amount: number;
+  amount: number | string;  // 支持字符串或数字
   memo?: string;
   operatorId: string;
   operatorName?: string;
@@ -106,7 +106,10 @@ export class SystemWithdrawalController {
     if (!dto.toAccountSequence) {
       throw new BadRequestException('接收账户不能为空');
     }
-    if (!dto.amount || dto.amount <= 0) {
+
+    // 将 amount 转换为数字（前端可能传入字符串）
+    const amount = typeof dto.amount === 'string' ? parseFloat(dto.amount) : dto.amount;
+    if (!amount || isNaN(amount) || amount <= 0) {
       throw new BadRequestException('转出金额必须大于0');
     }
     if (!dto.operatorId) {
@@ -116,7 +119,7 @@ export class SystemWithdrawalController {
     const result = await this.systemWithdrawalService.requestSystemWithdrawal({
       fromAccountSequence: dto.fromAccountSequence,
       toAccountSequence: dto.toAccountSequence,
-      amount: dto.amount,
+      amount: amount,
       memo: dto.memo,
       operatorId: dto.operatorId,
       operatorName: dto.operatorName,

frontend/admin-web/src/app/(dashboard)/system-transfer/page.tsx

@@ -117,8 +117,11 @@ export default function SystemTransferPage() {
       setFormErrors({});
       // 切换到订单列表查看
       setActiveTab('orders');
-    } catch (err) {
-      toast.error((err as Error).message || '划转失败');
+    } catch (err: unknown) {
+      // 从 Axios 错误中提取消息
+      const axiosError = err as { response?: { data?: { message?: string } }; message?: string };
+      const errorMessage = axiosError.response?.data?.message || axiosError.message || '划转失败';
+      toast.error(errorMessage);
     }
   };