feat(计费): 支持账号计费倍率快照与统计展示

- 新增 accounts.rate_multiplier（默认 1.0，允许 0）
- 使用 usage_logs.account_rate_multiplier 记录倍率快照，避免历史回算
- 统计/导出/管理端展示账号口径费用（total_cost * account_rate_multiplier）

backend/ent/usagelog/usagelog.go

@@ -54,6 +54,8 @@ const (
 	FieldActualCost = "actual_cost"
 	// FieldRateMultiplier holds the string denoting the rate_multiplier field in the database.
 	FieldRateMultiplier = "rate_multiplier"
+	// FieldAccountRateMultiplier holds the string denoting the account_rate_multiplier field in the database.
+	FieldAccountRateMultiplier = "account_rate_multiplier"
 	// FieldBillingType holds the string denoting the billing_type field in the database.
 	FieldBillingType = "billing_type"
 	// FieldStream holds the string denoting the stream field in the database.
@@ -144,6 +146,7 @@ var Columns = []string{
 	FieldTotalCost,
 	FieldActualCost,
 	FieldRateMultiplier,
+	FieldAccountRateMultiplier,
 	FieldBillingType,
 	FieldStream,
 	FieldDurationMs,
@@ -320,6 +323,11 @@ func ByRateMultiplier(opts ...sql.OrderTermOption) OrderOption {
 	return sql.OrderByField(FieldRateMultiplier, opts...).ToFunc()
 }
 
+// ByAccountRateMultiplier orders the results by the account_rate_multiplier field.
+func ByAccountRateMultiplier(opts ...sql.OrderTermOption) OrderOption {
+	return sql.OrderByField(FieldAccountRateMultiplier, opts...).ToFunc()
+}
+
 // ByBillingType orders the results by the billing_type field.
 func ByBillingType(opts ...sql.OrderTermOption) OrderOption {
 	return sql.OrderByField(FieldBillingType, opts...).ToFunc()

backend/ent/usagelog/where.go

@@ -155,6 +155,11 @@ func RateMultiplier(v float64) predicate.UsageLog {
 	return predicate.UsageLog(sql.FieldEQ(FieldRateMultiplier, v))
 }
 
+// AccountRateMultiplier applies equality check predicate on the "account_rate_multiplier" field. It's identical to AccountRateMultiplierEQ.
+func AccountRateMultiplier(v float64) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldEQ(FieldAccountRateMultiplier, v))
+}
+
 // BillingType applies equality check predicate on the "billing_type" field. It's identical to BillingTypeEQ.
 func BillingType(v int8) predicate.UsageLog {
 	return predicate.UsageLog(sql.FieldEQ(FieldBillingType, v))
@@ -970,6 +975,56 @@ func RateMultiplierLTE(v float64) predicate.UsageLog {
 	return predicate.UsageLog(sql.FieldLTE(FieldRateMultiplier, v))
 }
 
+// AccountRateMultiplierEQ applies the EQ predicate on the "account_rate_multiplier" field.
+func AccountRateMultiplierEQ(v float64) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldEQ(FieldAccountRateMultiplier, v))
+}
+
+// AccountRateMultiplierNEQ applies the NEQ predicate on the "account_rate_multiplier" field.
+func AccountRateMultiplierNEQ(v float64) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldNEQ(FieldAccountRateMultiplier, v))
+}
+
+// AccountRateMultiplierIn applies the In predicate on the "account_rate_multiplier" field.
+func AccountRateMultiplierIn(vs ...float64) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldIn(FieldAccountRateMultiplier, vs...))
+}
+
+// AccountRateMultiplierNotIn applies the NotIn predicate on the "account_rate_multiplier" field.
+func AccountRateMultiplierNotIn(vs ...float64) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldNotIn(FieldAccountRateMultiplier, vs...))
+}
+
+// AccountRateMultiplierGT applies the GT predicate on the "account_rate_multiplier" field.
+func AccountRateMultiplierGT(v float64) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldGT(FieldAccountRateMultiplier, v))
+}
+
+// AccountRateMultiplierGTE applies the GTE predicate on the "account_rate_multiplier" field.
+func AccountRateMultiplierGTE(v float64) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldGTE(FieldAccountRateMultiplier, v))
+}
+
+// AccountRateMultiplierLT applies the LT predicate on the "account_rate_multiplier" field.
+func AccountRateMultiplierLT(v float64) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldLT(FieldAccountRateMultiplier, v))
+}
+
+// AccountRateMultiplierLTE applies the LTE predicate on the "account_rate_multiplier" field.
+func AccountRateMultiplierLTE(v float64) predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldLTE(FieldAccountRateMultiplier, v))
+}
+
+// AccountRateMultiplierIsNil applies the IsNil predicate on the "account_rate_multiplier" field.
+func AccountRateMultiplierIsNil() predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldIsNull(FieldAccountRateMultiplier))
+}
+
+// AccountRateMultiplierNotNil applies the NotNil predicate on the "account_rate_multiplier" field.
+func AccountRateMultiplierNotNil() predicate.UsageLog {
+	return predicate.UsageLog(sql.FieldNotNull(FieldAccountRateMultiplier))
+}
+
 // BillingTypeEQ applies the EQ predicate on the "billing_type" field.
 func BillingTypeEQ(v int8) predicate.UsageLog {
 	return predicate.UsageLog(sql.FieldEQ(FieldBillingType, v))