fix(billing): surface quota saturation events for admin auditing

Thread int32 saturation clamps from tiered settlement and video task
recompute into the consume/task logs under admin_info, so oversized or
malformed billing inputs stay auditable. Clamp negative audio duration
before token conversion and gate the saturation UI markers on admin.

relay/common/relay_info.go

@@ -163,6 +163,11 @@ type RelayInfo struct {
 
 	PriceData types.PriceData
 
+	// QuotaClamp is set (non-nil) when a quota conversion saturated at the
+	// int32 bound (or NaN fallback) while computing this request's charge.
+	// It is surfaced onto the consume/task log's admin_info for auditing.
+	QuotaClamp *common.QuotaClamp
+
 	// TieredBillingSnapshot is a frozen snapshot of tiered billing rules
 	// captured at pre-consume time. Non-nil only when billing mode is "tiered_expr".
 	TieredBillingSnapshot *billingexpr.BillingSnapshot