fix(user-billing): add pool env parser (#1950)

internal/userbilling/service.go

@@ -2921,6 +2921,18 @@ func parseInt64(value string, fallback int64) int64 {
 	return parsed
 }
 
+func envInt(name string, fallback int) int {
+	value := strings.TrimSpace(os.Getenv(name))
+	if value == "" {
+		return fallback
+	}
+	parsed, err := strconv.Atoi(value)
+	if err != nil || parsed <= 0 {
+		return fallback
+	}
+	return parsed
+}
+
 func parseDurationHours(value string, fallbackHours int64) time.Duration {
 	return time.Duration(parseInt64(value, fallbackHours)) * time.Hour
 }