refactor: align tariff builder with bot functionality

- Remove unused fields: custom_days, custom_traffic (bot doesn't use them)
- Add promo groups selection to tariff form
- Add API endpoint for fetching available promo groups
- Make traffic topup packages dynamic (add/remove any number)
- Fix stuck 0 in number inputs when clearing
- Add validation messages explaining why save button is blocked
- Match bot validation: name 2-50 chars, device_limit >= 1, tier_level 1-10
- Add missing i18n translations for new fields and validation errors

src/locales/zh.json

@@ -1059,6 +1059,7 @@
       "nameLabel": "套餐名称",
       "nameExamplePeriod": "例如：标准",
       "nameExampleDaily": "例如：日套餐",
+      "nameHint": "2到50个字符",
       "descriptionLabel": "描述",
       "trafficLimitLabel": "流量限制",
       "gbUnit": "GB",
@@ -1074,8 +1075,12 @@
       "addButton": "添加",
       "noPeriodsHint": "没有添加的周期。请至少添加一个周期。",
       "daysShort": "天",
+      "serversTitle": "服务器",
       "serversTabHint": "选择此套餐上可用的服务器。",
       "noServersAvailable": "没有可用的服务器",
+      "promoGroupsTitle": "促销组",
+      "promoGroupsHint": "选择可以访问此套餐的促销组。如果未选择任何组，则所有人都可以访问。",
+      "noPromoGroups": "没有促销组",
       "extraDeviceTitle": "额外设备",
       "devicePriceLabel": "设备价格（30天）：",
       "devicePriceHint": "0 = 无法购买设备",
@@ -1085,6 +1090,8 @@
       "trafficMaxLimitLabel": "最大限制：",
       "trafficLimitHint2": "（0 = 无限制）",
       "trafficPackagesLabel": "流量包：",
+      "addPackageTitle": "添加流量包",
+      "noPackagesHint": "没有添加流量包。请至少添加一个流量包。",
       "gbPackageUnit": "GB：",
       "customDaysTitle": "自定义天数",
       "customDaysDesc": "用户自行选择订阅期限",
@@ -1116,7 +1123,18 @@
       "dailyPriceLabel": "每天价格",
       "currencyPerDay": "₽/天",
       "dailyDeductionDesc": "每天从用户余额中扣除",
-      "dailyPriceRequired": "请输入大于0的每日价格"
+      "dailyPriceRequired": "请输入大于0的每日价格",
+      "cannotSave": "无法保存套餐：",
+      "validation": {
+        "nameRequired": "请输入套餐名称",
+        "nameLength": "名称必须为2到50个字符",
+        "deviceLimitRequired": "请指定设备数量（至少1个）",
+        "tierLevelInvalid": "等级必须在1到10之间",
+        "fieldsRequired": "请填写必填字段（设备数、等级）",
+        "periodsRequired": "请添加至少一个期限",
+        "dailyPriceRequired": "请输入大于0的每日价格",
+        "trafficPackagesRequired": "请添加至少一个流量包（或关闭流量购买）"
+      }
     },
     "servers": {
       "title": "服务器管理",