fix(frontend): unify purchase icon with subscriptions (CreditCardIcon)

Use the same CreditCardIcon for both "我的订阅" and "充值/订阅" sidebar
items. Remove unused RechargeSubscriptionIcon.

frontend/src/components/layout/AppSidebar.vue

@@ -355,21 +355,6 @@ const CreditCardIcon = {
     )
 }
 
-const RechargeSubscriptionIcon = {
-  render: () =>
-    h(
-      'svg',
-      { fill: 'none', viewBox: '0 0 24 24', stroke: 'currentColor', 'stroke-width': '1.5' },
-      [
-        h('path', {
-          'stroke-linecap': 'round',
-          'stroke-linejoin': 'round',
-          d: 'M2.25 18.75a60.07 60.07 0 0 1 15.797 2.101c.727.198 1.453-.342 1.453-1.096V18.75M3.75 4.5v.75A.75.75 0 0 1 3 6h-.75m0 0v-.375c0-.621.504-1.125 1.125-1.125H20.25M2.25 6v9m18-10.5v.75c0 .414.336.75.75.75h.75m-1.5-1.5h.375c.621 0 1.125.504 1.125 1.125v9.75c0 .621-.504 1.125-1.125 1.125h-.375m1.5-1.5H21a.75.75 0 0 0-.75.75v.75m0 0H3.75m0 0h-.375a1.125 1.125 0 0 1-1.125-1.125V15m1.5 1.5v-.75A.75.75 0 0 0 3 15h-.75M15 10.5a3 3 0 1 1-6 0 3 3 0 0 1 6 0Zm3 0h.008v.008H18V10.5Zm-12 0h.008v.008H6V10.5Z'
-        })
-      ]
-    )
-}
-
 const GlobeIcon = {
   render: () =>
     h(
@@ -568,7 +553,7 @@ const userNavItems = computed((): NavItem[] => {
           {
             path: '/purchase',
             label: t('nav.buySubscription'),
-            icon: RechargeSubscriptionIcon,
+            icon: CreditCardIcon,
             hideInSimpleMode: true
           },
         ]
@@ -606,7 +591,7 @@ const personalNavItems = computed((): NavItem[] => {
           {
             path: '/purchase',
             label: t('nav.buySubscription'),
-            icon: RechargeSubscriptionIcon,
+            icon: CreditCardIcon,
             hideInSimpleMode: true
           },
         ]