fix: allow clearing number inputs and add validation

- Add inputHelpers utility for number inputs that allow empty values
- Update tariff, campaign, promo offers, and server forms
- Add validation for required fields (deviceLimit, tierLevel, dailyPrice)
- Add placeholders and error indicators for empty required fields
- Add fieldRequired and dailyPriceRequired translations

src/locales/en.json

@@ -1259,6 +1259,7 @@
       "deviceLimitLabel": "Devices in tariff",
       "tierLevelLabel": "Tariff tier level",
       "tierLevelHint": "Affects upgrade availability between tariffs",
+      "fieldRequired": "Required field",
       "periodsTabHint": "Add periods and prices for the tariff. Users will be able to choose from the added periods.",
       "addPeriodTitle": "Add period",
       "daysLabel": "Days",
@@ -1307,7 +1308,8 @@
       "periodType": "Period-based",
       "dailyPriceLabel": "Price per day",
       "currencyPerDay": "\u20bd/day",
-      "dailyDeductionDesc": "Charged daily from user's balance"
+      "dailyDeductionDesc": "Charged daily from user's balance",
+      "dailyPriceRequired": "Enter a price per day greater than 0"
     },
     "servers": {
       "title": "Server Management",

src/locales/fa.json

@@ -1029,6 +1029,7 @@
       "deviceLimitLabel": "دستگاه‌ها در تعرفه",
       "tierLevelLabel": "سطح تعرفه",
       "tierLevelHint": "بر دسترسی ارتقا بین تعرفه‌ها تأثیر می‌گذارد",
+      "fieldRequired": "فیلد اجباری",
       "periodsTabHint": "دوره‌ها و قیمت‌ها را برای تعرفه اضافه کنید. کاربران می‌توانند از دوره‌های اضافه شده انتخاب کنند.",
       "addPeriodTitle": "افزودن دوره",
       "daysLabel": "روز",
@@ -1077,7 +1078,8 @@
       "periodType": "دوره‌ای",
       "dailyPriceLabel": "قیمت روزانه",
       "currencyPerDay": "₽/روز",
-      "dailyDeductionDesc": "هر روز از موجودی کاربر کسر می‌شود"
+      "dailyDeductionDesc": "هر روز از موجودی کاربر کسر می‌شود",
+      "dailyPriceRequired": "قیمت روزانه بزرگتر از 0 را وارد کنید"
     },
     "servers": {
       "title": "مدیریت سرورها",

src/locales/ru.json

@@ -1770,6 +1770,7 @@
       "deviceLimitLabel": "Устройств в тарифе",
       "tierLevelLabel": "Уровень тарифа",
       "tierLevelHint": "Влияет на доступность перехода между тарифами",
+      "fieldRequired": "Обязательное поле",
       "periodsTabHint": "Добавьте периоды и цены для тарифа. Пользователи смогут выбирать из добавленных периодов.",
       "addPeriodTitle": "Добавить период",
       "daysLabel": "Дней",
@@ -1818,7 +1819,8 @@
       "periodType": "Периодный",
       "dailyPriceLabel": "Цена за день",
       "currencyPerDay": "₽/день",
-      "dailyDeductionDesc": "Списывается ежедневно с баланса пользователя"
+      "dailyDeductionDesc": "Списывается ежедневно с баланса пользователя",
+      "dailyPriceRequired": "Укажите цену за день больше 0"
     },
     "servers": {
       "title": "Управление серверами",

src/locales/zh.json

@@ -1066,6 +1066,7 @@
       "deviceLimitLabel": "套餐中的设备数",
       "tierLevelLabel": "套餐等级",
       "tierLevelHint": "影响套餐之间的升级可用性",
+      "fieldRequired": "必填字段",
       "periodsTabHint": "为套餐添加周期和价格。用户将能够从添加的周期中选择。",
       "addPeriodTitle": "添加周期",
       "daysLabel": "天",
@@ -1114,7 +1115,8 @@
       "periodType": "周期套餐",
       "dailyPriceLabel": "每天价格",
       "currencyPerDay": "₽/天",
-      "dailyDeductionDesc": "每天从用户余额中扣除"
+      "dailyDeductionDesc": "每天从用户余额中扣除",
+      "dailyPriceRequired": "请输入大于0的每日价格"
     },
     "servers": {
       "title": "服务器管理",