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/account/where.go

@@ -105,6 +105,11 @@ func Priority(v int) predicate.Account {
 	return predicate.Account(sql.FieldEQ(FieldPriority, v))
 }
 
+// RateMultiplier applies equality check predicate on the "rate_multiplier" field. It's identical to RateMultiplierEQ.
+func RateMultiplier(v float64) predicate.Account {
+	return predicate.Account(sql.FieldEQ(FieldRateMultiplier, v))
+}
+
 // Status applies equality check predicate on the "status" field. It's identical to StatusEQ.
 func Status(v string) predicate.Account {
 	return predicate.Account(sql.FieldEQ(FieldStatus, v))
@@ -675,6 +680,46 @@ func PriorityLTE(v int) predicate.Account {
 	return predicate.Account(sql.FieldLTE(FieldPriority, v))
 }
 
+// RateMultiplierEQ applies the EQ predicate on the "rate_multiplier" field.
+func RateMultiplierEQ(v float64) predicate.Account {
+	return predicate.Account(sql.FieldEQ(FieldRateMultiplier, v))
+}
+
+// RateMultiplierNEQ applies the NEQ predicate on the "rate_multiplier" field.
+func RateMultiplierNEQ(v float64) predicate.Account {
+	return predicate.Account(sql.FieldNEQ(FieldRateMultiplier, v))
+}
+
+// RateMultiplierIn applies the In predicate on the "rate_multiplier" field.
+func RateMultiplierIn(vs ...float64) predicate.Account {
+	return predicate.Account(sql.FieldIn(FieldRateMultiplier, vs...))
+}
+
+// RateMultiplierNotIn applies the NotIn predicate on the "rate_multiplier" field.
+func RateMultiplierNotIn(vs ...float64) predicate.Account {
+	return predicate.Account(sql.FieldNotIn(FieldRateMultiplier, vs...))
+}
+
+// RateMultiplierGT applies the GT predicate on the "rate_multiplier" field.
+func RateMultiplierGT(v float64) predicate.Account {
+	return predicate.Account(sql.FieldGT(FieldRateMultiplier, v))
+}
+
+// RateMultiplierGTE applies the GTE predicate on the "rate_multiplier" field.
+func RateMultiplierGTE(v float64) predicate.Account {
+	return predicate.Account(sql.FieldGTE(FieldRateMultiplier, v))
+}
+
+// RateMultiplierLT applies the LT predicate on the "rate_multiplier" field.
+func RateMultiplierLT(v float64) predicate.Account {
+	return predicate.Account(sql.FieldLT(FieldRateMultiplier, v))
+}
+
+// RateMultiplierLTE applies the LTE predicate on the "rate_multiplier" field.
+func RateMultiplierLTE(v float64) predicate.Account {
+	return predicate.Account(sql.FieldLTE(FieldRateMultiplier, v))
+}
+
 // StatusEQ applies the EQ predicate on the "status" field.
 func StatusEQ(v string) predicate.Account {
 	return predicate.Account(sql.FieldEQ(FieldStatus, v))