feat: add ButtonsTab for per-section button style customization

Visual editor in admin settings for configuring Telegram button colors
and custom emoji IDs per menu section. Includes API client, draft state
management, save/reset, and translations for ru/en/fa/zh locales.

src/pages/AdminSettings.tsx

@@ -9,6 +9,7 @@ import { MENU_SECTIONS, MenuItem, formatSettingKey } from '../components/admin';
 import { usePlatform } from '../platform/hooks/usePlatform';
 import { AnalyticsTab } from '../components/admin/AnalyticsTab';
 import { BrandingTab } from '../components/admin/BrandingTab';
+import { ButtonsTab } from '../components/admin/ButtonsTab';
 import { ThemeTab } from '../components/admin/ThemeTab';
 import { FavoritesTab } from '../components/admin/FavoritesTab';
 import { SettingsTab } from '../components/admin/SettingsTab';
@@ -174,6 +175,8 @@ export default function AdminSettings() {
         return <BrandingTab accentColor={themeColors?.accent} />;
       case 'theme':
         return <ThemeTab />;
+      case 'buttons':
+        return <ButtonsTab />;
       case 'favorites':
         return (
           <FavoritesTab