fix(billing): validate quantity parameters and harden quota calculations

Bound user-supplied count/duration parameters at request validation,
route ratio multipliers through guarded setters, and use saturating
int conversions in all quota math paths.

relay/channel/task/gemini/billing.go

@@ -3,6 +3,8 @@ package gemini
 import (
 	"strconv"
 	"strings"
+
+	relaycommon "github.com/QuantumNous/new-api/relay/common"
 )
 
 // ParseVeoDurationSeconds extracts durationSeconds from metadata.
@@ -46,19 +48,21 @@ func ParseVeoResolution(metadata map[string]any) string {
 
 // ResolveVeoDuration returns the effective duration in seconds.
 // Priority: metadata["durationSeconds"] > stdDuration > stdSeconds > default (8).
+// The result is capped because it is used as a billing multiplier and the
+// metadata path bypasses standard request validation.
 func ResolveVeoDuration(metadata map[string]any, stdDuration int, stdSeconds string) int {
 	if metadata != nil {
 		if _, exists := metadata["durationSeconds"]; exists {
 			if d := ParseVeoDurationSeconds(metadata); d > 0 {
-				return d
+				return min(d, relaycommon.MaxTaskDurationSeconds)
 			}
 		}
 	}
 	if stdDuration > 0 {
-		return stdDuration
+		return min(stdDuration, relaycommon.MaxTaskDurationSeconds)
 	}
 	if s, err := strconv.Atoi(stdSeconds); err == nil && s > 0 {
-		return s
+		return min(s, relaycommon.MaxTaskDurationSeconds)
 	}
 	return 8
 }