feat: extract promocodes and promo groups into separate pages

- Add AdminPromocodeCreate page for creating/editing promocodes
- Add AdminPromoGroups page for listing discount groups
- Add AdminPromoGroupCreate page for creating/editing discount groups
- Move promo groups from Promocodes section to separate admin section
- Simplify AdminPromocodes by removing embedded modals and groups tab
- Add routes and navigation for new pages
- Add i18n keys for all 4 locales (ru, en, zh, fa)

src/pages/AdminPanel.tsx

@@ -134,6 +134,16 @@ const GiftIcon = () => (
   </svg>
 );
 
+const UserGroupIcon = () => (
+  <svg className="h-5 w-5" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={1.5}>
+    <path
+      strokeLinecap="round"
+      strokeLinejoin="round"
+      d="M18 18.72a9.094 9.094 0 003.741-.479 3 3 0 00-4.682-2.72m.94 3.198l.001.031c0 .225-.012.447-.037.666A11.944 11.944 0 0112 21c-2.17 0-4.207-.576-5.963-1.584A6.062 6.062 0 016 18.719m12 0a5.971 5.971 0 00-.941-3.197m0 0A5.995 5.995 0 0012 12.75a5.995 5.995 0 00-5.058 2.772m0 0a3 3 0 00-4.681 2.72 8.986 8.986 0 003.74.477m.94-3.197a5.971 5.971 0 00-.94 3.197M15 6.75a3 3 0 11-6 0 3 3 0 016 0zm6 3a2.25 2.25 0 11-4.5 0 2.25 2.25 0 014.5 0zm-13.5 0a2.25 2.25 0 11-4.5 0 2.25 2.25 0 014.5 0z"
+    />
+  </svg>
+);
+
 const MegaphoneIcon = () => (
   <svg className="h-5 w-5" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={1.5}>
     <path
@@ -368,6 +378,12 @@ export default function AdminPanel() {
           title: t('admin.nav.promocodes'),
           description: t('admin.panel.promocodesDesc'),
         },
+        {
+          to: '/admin/promo-groups',
+          icon: <UserGroupIcon />,
+          title: t('admin.nav.promoGroups'),
+          description: t('admin.panel.promoGroupsDesc'),
+        },
         {
           to: '/admin/promo-offers',
           icon: <GiftIcon />,