refactor: move campaign editing from modal to separate page

- Create AdminCampaignEdit page for editing campaigns
- Remove CampaignModal from AdminCampaigns
- Use centralized icons (CampaignIcon, ChartIcon added)
- Add route /admin/campaigns/:id/edit
- Add localization keys for loadError and updateError

src/locales/en.json

@@ -1489,7 +1489,9 @@
         "deleteText": "This action cannot be undone. Campaigns with registrations cannot be deleted.",
         "cancel": "Cancel",
         "delete": "Delete"
-      }
+      },
+      "loadError": "Failed to load campaign",
+      "updateError": "Failed to save changes"
     },
     "promocodes": {
       "title": "Promo Codes",

src/locales/fa.json

@@ -1282,7 +1282,9 @@
         "deleteText": "این عمل قابل بازگشت نیست. کمپین‌هایی که ثبت‌نام دارند قابل حذف نیستند.",
         "cancel": "لغو",
         "delete": "حذف"
-      }
+      },
+      "loadError": "بارگذاری کمپین ناموفق بود",
+      "updateError": "ذخیره تغییرات ناموفق بود"
     },
     "promocodes": {
       "title": "کدهای تخفیف",

src/locales/ru.json

@@ -2000,7 +2000,9 @@
         "deleteText": "Это действие нельзя отменить. Кампании с регистрациями удалить нельзя.",
         "cancel": "Отмена",
         "delete": "Удалить"
-      }
+      },
+      "loadError": "Не удалось загрузить кампанию",
+      "updateError": "Не удалось сохранить изменения"
     },
     "promocodes": {
       "title": "Промокоды",

src/locales/zh.json

@@ -1281,7 +1281,9 @@
         "deleteText": "此操作不可撤销。有注册记录的活动无法删除。",
         "cancel": "取消",
         "delete": "删除"
-      }
+      },
+      "loadError": "加载活动失败",
+      "updateError": "保存更改失败"
     },
     "promocodes": {
       "title": "促销码",