Order模块：完成分字段重构

核心改造：
1. DTO层全部改为*Cent int64字段（OrderDTO/CheckoutDTO/RefundStatusDTO）
2. 内部结构体orderPricing和checkoutSettlement改为分字段
3. calculateCheckoutSettlement函数改为返回分单位
4. 所有wallet.AppendEntries调用改为AmountCent
5. toAdminDTO/toCheckoutAdminDTO转换函数使用*Cent字段
6. applyOrderPriceView/applyCheckoutPriceView使用分字段
7. buildOrderPricing返回分单位
8. 订单取消/关闭/退款使用分字段计算

技术细节：
- 删除了3处float64金额相加后转分的逻辑
- calculateCheckoutSettlement内部仍用元计算保持兼容性，最后转为分
- 新增effectiveDepositOriginalAmountCent辅助函数
- buildRefundStatusDTO使用TotalAmountCent
- 编译验证通过 ✅

backend/internal/modules/adminuser/repository_test.go

@@ -0,0 +1,35 @@
+package adminuser
+
+import "testing"
+
+func TestDepositFreeQuotaAmountCent(t *testing.T) {
+	tests := []struct {
+		name string
+		req  DepositFreeQuotaRequest
+		want int64
+	}{
+		{
+			name: "优先使用分字段",
+			req:  DepositFreeQuotaRequest{AmountCent: 1234, Amount: 99},
+			want: 1234,
+		},
+		{
+			name: "缺少分字段时回退元字段",
+			req:  DepositFreeQuotaRequest{Amount: 12.34},
+			want: 1234,
+		},
+		{
+			name: "负分拒绝",
+			req:  DepositFreeQuotaRequest{AmountCent: -1, Amount: 12.34},
+			want: -1,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := depositFreeQuotaAmountCent(tt.req); got != tt.want {
+				t.Fatalf("depositFreeQuotaAmountCent() = %d, want %d", got, tt.want)
+			}
+		})
+	}
+}