货币体系: 全平台统一使用积分(POINT)替代人民币(CNY)

后端:
- 模型 currency 默认值 CNY→POINT (MerchantProduct/WalletAccount/FulfillmentOrder)
- DashboardStats TotalSales/TotalFees 从 float64 改为 int64，去掉 /100.0 转换
- 上游 OpenOrderQuery.Amount 从 float64 改为 int64，直接返回积分整数
- 钱包/商品创建时 currency 默认 POINT

前端:
- 去掉 centsToYuan/yuanToCents 转换函数，金额直接用整数积分
- money() 显示从 ¥X.XX 改为 X 积分
- 商品售价/成本表单字段名改回 price_amount/cost_amount，precision 改 0
- 钱包调整表单 amount_yuan→amount，precision 改 0
- 手续费固定金额表单 precision 改 0，label 改积分
- 币种选项 CNY→POINT
- Dashboard 成交金额/手续费 suffix 元→积分，去掉 precision

数据库:
- 新增迁移 004: currency 默认值 CNY→POINT，存量数据更新

backend/internal/service/fulfillment.go

@@ -581,12 +581,12 @@ func orderCallbackData(order *model.FulfillmentOrder) map[string]interface{} {
 
 // DashboardStats 仪表盘聚合指标。
 type DashboardStats struct {
-	ProductCount      int64   `json:"product_count"`
-	MerchantCount     int64   `json:"merchant_count"`
-	OrderCount        int64   `json:"order_count"`
-	TotalSales        float64 `json:"total_sales"`
-	TotalFees         float64 `json:"total_fees"`
-	PendingOrderCount int64   `json:"pending_order_count"`
+	ProductCount      int64 `json:"product_count"`
+	MerchantCount     int64 `json:"merchant_count"`
+	OrderCount        int64 `json:"order_count"`
+	TotalSales        int64 `json:"total_sales"`
+	TotalFees         int64 `json:"total_fees"`
+	PendingOrderCount int64 `json:"pending_order_count"`
 }
 
 // Dashboard 汇总商户维度的商品、商户、订单与金额统计。
@@ -605,11 +605,11 @@ func (s *FulfillmentService) Dashboard(merchantID uint, isPlatformAdmin bool) (*
 	s.db.Model(&model.FulfillmentOrder{}).
 		Where("merchant_id = ?", merchantID).
 		Where("payment_status = ?", model.PaymentStatusPaid).
-		Select("COALESCE(SUM(amount),0) / 100.0").Scan(&stats.TotalSales)
+		Select("COALESCE(SUM(amount),0)").Scan(&stats.TotalSales)
 	s.db.Model(&model.FulfillmentOrder{}).
 		Where("merchant_id = ?", merchantID).
 		Where("payment_status = ?", model.PaymentStatusPaid).
-		Select("COALESCE(SUM(service_fee_amount),0) / 100.0").Scan(&stats.TotalFees)
+		Select("COALESCE(SUM(service_fee_amount),0)").Scan(&stats.TotalFees)
 	return stats, nil
 }
 
@@ -623,7 +623,7 @@ type OpenOrderQuery struct {
 	CannotShipReason string            `json:"cannot_ship_reason,omitempty"`
 	Product          *OpenOrderProduct `json:"product,omitempty"`
 	BuyerName        string            `json:"buyer_name"`
-	Amount           float64           `json:"amount"`
+	Amount           int64             `json:"amount"`
 	ProviderOrderNo  string            `json:"provider_order_no,omitempty"`
 	CreatedAt        time.Time         `json:"created_at"`
 	ShippedAt        *time.Time        `json:"shipped_at"`
@@ -691,7 +691,7 @@ func (s *FulfillmentService) QueryOpenOrder(orderNo string) (*OpenOrderQuery, er
 		CanShip:          canShip,
 		CannotShipReason: reason,
 		BuyerName:        order.BuyerReference,
-		Amount:           float64(order.Amount) / 100.0,
+		Amount:           order.Amount,
 		ProviderOrderNo:  order.ProviderOrderNo,
 		CreatedAt:        order.CreatedAt,
 		ShippedAt:        order.DeliveredAt,

backend/internal/service/fulfillment_test.go

@@ -32,7 +32,7 @@ func seedFulfillmentMerchant(t *testing.T, db *gorm.DB, code string, balance, st
 	}
 	if err := db.Create(&model.WalletAccount{
 		MerchantID:       merchant.ID,
-		Currency:         "CNY",
+		Currency:         "POINT",
 		AvailableBalance: balance,
 	}).Error; err != nil {
 		t.Fatalf("create wallet: %v", err)
@@ -47,7 +47,7 @@ func seedFulfillmentMerchant(t *testing.T, db *gorm.DB, code string, balance, st
 		SKU:         "sku-basic",
 		DisplayName: "测试商品",
 		PriceAmount: price,
-		Currency:    "CNY",
+		Currency:    "POINT",
 		Stock:       stock,
 		Status:      model.ProductStatusActive,
 	}

backend/internal/service/merchant.go

@@ -91,7 +91,7 @@ func (s *MerchantService) CreateMerchant(in CreateMerchantInput, actorUserID uin
 		if err := tx.Create(merchant).Error; err != nil {
 			return err
 		}
-		if err := tx.Create(&model.WalletAccount{MerchantID: merchant.ID, Currency: "CNY"}).Error; err != nil {
+	if err := tx.Create(&model.WalletAccount{MerchantID: merchant.ID, Currency: "POINT"}).Error; err != nil {
 			return err
 		}
 		if err := tx.Create(&model.MerchantMember{
@@ -332,7 +332,7 @@ func (s *MerchantService) CreateMerchantProduct(merchantID uint, in CreateMercha
 		return nil, errors.New("库存只能为 -1 或非负整数")
 	}
 	if in.Currency == "" {
-		in.Currency = "CNY"
+		in.Currency = "POINT"
 	}
 	in.Currency = strings.ToUpper(in.Currency)
 	if in.Status == "" {