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.

pkg/billingexpr/types.go

@@ -3,6 +3,8 @@ package billingexpr
 import (
 	"crypto/sha256"
 	"fmt"
+
+	"github.com/QuantumNous/new-api/common"
 )
 
 type RequestInput struct {
@@ -57,6 +59,11 @@ type TieredResult struct {
 	ActualQuotaAfterGroup  int     `json:"actual_quota_after_group"`
 	MatchedTier            string  `json:"matched_tier"`
 	CrossedTier            bool    `json:"crossed_tier"`
+	// Clamp records an int32 saturation event during quota conversion so the
+	// caller can surface it on the consume log for admin auditing. Nil when no
+	// clamping occurred. Not serialized: the marker is attached separately via
+	// the shared quota-saturation audit path.
+	Clamp *common.QuotaClamp `json:"-"`
 }
 
 // ExprHashString returns the SHA-256 hex digest of an expression string.