feat: Linear-style UI redesign with improved mobile experience

Major changes:
- Redesign cabinet with Linear-style components and top navigation
- Replace detail modals with dedicated pages (users, broadcasts, email templates)
- Add email channel support for broadcasts
- Remove pull-to-refresh, improve drag-and-drop on touch devices
- Fix Telegram Mini App: fullscreen, back button, scroll restoration
- Unify admin pages color scheme to design system
- Mobile-first improvements: horizontal tabs for settings, better touch targets

src/locales/en.json

@@ -28,7 +28,8 @@
       "perGb": "/GB"
     },
     "retry": "Retry",
-    "saving": "Saving..."
+    "saving": "Saving...",
+    "understand": "Got it"
   },
   "nav": {
     "dashboard": "Dashboard",
@@ -761,7 +762,9 @@
       "resetted": "Template reset to default",
       "testSent": "Test email sent",
       "variables": "Available Variables",
-      "clickToCopy": "Click to copy"
+      "clickToCopy": "Click to copy",
+      "previewDesktopOnly": "Preview is only available in the desktop web version",
+      "previewNotAvailable": "Preview not available"
     },
     "payments": {
       "title": "Payment verification",

src/locales/fa.json

@@ -28,7 +28,8 @@
     "add": "افزودن",
     "refresh": "بازخوانی",
     "retry": "تلاش مجدد",
-    "saving": "در حال ذخیره..."
+    "saving": "در حال ذخیره...",
+    "understand": "متوجه شدم"
   },
   "nav": {
     "dashboard": "داشبورد",
@@ -667,7 +668,9 @@
       "resetted": "قالب به پیش‌فرض بازگردانده شد",
       "testSent": "ایمیل آزمایشی ارسال شد",
       "variables": "متغیرهای موجود",
-      "clickToCopy": "برای کپی کلیک کنید"
+      "clickToCopy": "برای کپی کلیک کنید",
+      "previewDesktopOnly": "پیش‌نمایش فقط در نسخه وب دسکتاپ در دسترس است",
+      "previewNotAvailable": "پیش‌نمایش در دسترس نیست"
     },
     "wheel": {
       "title": "تنظیمات چرخ شانس",

src/locales/ru.json

@@ -25,6 +25,7 @@
     "copy": "Копировать",
     "retry": "Повторить",
     "saving": "Сохранение...",
+    "understand": "Понятно",
     "units": {
       "gb": "ГБ",
       "perGb": "/ГБ"
@@ -777,7 +778,9 @@
       "resetted": "Шаблон сброшен к значению по умолчанию",
       "testSent": "Тестовое письмо отправлено",
       "variables": "Доступные переменные",
-      "clickToCopy": "Нажмите для копирования"
+      "clickToCopy": "Нажмите для копирования",
+      "previewDesktopOnly": "Предпросмотр доступен только в веб-версии на десктопе",
+      "previewNotAvailable": "Предпросмотр недоступен"
     },
     "payments": {
       "title": "Проверка платежей",

src/locales/zh.json

@@ -25,6 +25,7 @@
     "refresh": "刷新",
     "retry": "重试",
     "saving": "保存中...",
+    "understand": "明白了",
     "units": {
       "gb": "GB",
       "perGb": "/GB"
@@ -705,7 +706,9 @@
       "resetted": "模板已恢复默认",
       "testSent": "测试邮件已发送",
       "variables": "可用变量",
-      "clickToCopy": "点击复制"
+      "clickToCopy": "点击复制",
+      "previewDesktopOnly": "预览仅在桌面网页版可用",
+      "previewNotAvailable": "预览不可用"
     },
     "payments": {
       "title": "支付验证",