refactor: convert promocode stats modal to separate page

- Create AdminPromocodeStats.tsx with responsive mobile layout
- Add route /admin/promocodes/:id/stats
- Fix mobile layout in AdminPromocodes.tsx (badges and buttons no longer overlap)
- Remove PromocodeStatsModal component

src/locales/en.json

@@ -1540,6 +1540,8 @@
         "save": "Save"
       },
       "stats": {
+        "title": "Promo code statistics",
+        "notFound": "Promo code not found",
         "totalUses": "Total uses",
         "today": "Today",
         "remaining": "Remaining",

src/locales/fa.json

@@ -1333,6 +1333,8 @@
         "save": "ذخیره"
       },
       "stats": {
+        "title": "آمار کد تخفیف",
+        "notFound": "کد تخفیف یافت نشد",
         "totalUses": "کل استفاده‌ها",
         "today": "امروز",
         "remaining": "باقی‌مانده",

src/locales/ru.json

@@ -2051,6 +2051,8 @@
         "save": "Сохранить"
       },
       "stats": {
+        "title": "Статистика промокода",
+        "notFound": "Промокод не найден",
         "totalUses": "Всего использований",
         "today": "Сегодня",
         "remaining": "Осталось",

src/locales/zh.json

@@ -1332,6 +1332,8 @@
         "save": "保存"
       },
       "stats": {
+        "title": "促销码统计",
+        "notFound": "未找到促销码",
         "totalUses": "总使用次数",
         "today": "今天",
         "remaining": "剩余",