feat(v2): 多币种 product(ProductPrice 分币价目 + v1 元回退)+ 结算币种由渠道能力驱动

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013nMthbVEmQquxBRKb9Fj8u

internal/model/testdb.go

@@ -26,7 +26,8 @@ func OpenTestDB(t *testing.T) *gorm.DB {
 	if err != nil {
 		t.Fatalf("open test db: %v", err)
 	}
-	if err := db.AutoMigrate(&OrderV2{}, &Attempt{}, &Account{}, &Refund{}, &WebhookDelivery{}); err != nil {
+	if err := db.AutoMigrate(&OrderV2{}, &Attempt{}, &Account{}, &Refund{}, &WebhookDelivery{},
+		&Product{}, &ProductPrice{}); err != nil {
 		t.Fatalf("migrate: %v", err)
 	}
 	sqlDB, _ := db.DB()