fix(routing): show the Balancer label on mobile rule cards (#6960)

RuleCardList labelled balancer rules with t('pages.xray.balancer'), which is an object in every locale, so phones showed i18next's 'returned an object instead of string' error. It now uses the pages.xray.rules.balancer leaf the Balancers tab already uses, and the dead-keys test fails on any literal key that names a group.

frontend/src/pages/xray/routing/RuleCardList.tsx

@@ -152,9 +152,7 @@ export default function RuleCardList({
               <span className="flow-arrow">→</span>
               <div className="flow-side flow-side-target">
                 <span className="flow-label">
-                  {rule.balancerTag
-                    ? t('pages.xray.balancer') || 'Balancer'
-                    : t('pages.xray.Outbounds')}
+                  {rule.balancerTag ? t('pages.xray.rules.balancer') : t('pages.xray.Outbounds')}
                 </span>
                 {rule.outboundTag ? (
                   <Tag color="green" className="flow-tag">