feat: мультиязычные лендинги + переключатель языка + исправления по ревью

Мультиязычность:
- LanguageSwitcher на публичной странице покупки
- Вкладки локалей в админ-редакторе (ru/en/zh/fa)
- LocaleTabs и LocalizedInput компоненты
- Типы: LocaleDict, AdminLandingFeature, toLocaleDict хелпер
- ?lang= параметр при запросе конфига лендинга

Исправления по ревью:
- contentIndicators включает все локализуемые поля
- LocaleTabs вынесен над секциями аккордеона
- text-left → text-start для RTL
- nonEmptyDict: защита от undefined
- featureIds/methodIds обёрнуты в useMemo
- toggleSection/updateFeature* обёрнуты в useCallback
- formatPrice вынесен в shared utils/format.ts
- RTL через LOCALE_META.rtl вместо хардкода
- Переводы zh/fa для валидации и landing
- Variable shadowing: t → tariff

src/components/admin/LocaleTabs.tsx

@@ -0,0 +1,74 @@
+import { useTranslation } from 'react-i18next';
+import {
+  SUPPORTED_LOCALES,
+  LOCALE_META,
+  type SupportedLocale,
+  type LocaleDict,
+} from '../../api/landings';
+import { cn } from '../../lib/utils';
+
+interface LocaleTabsProps {
+  activeLocale: SupportedLocale;
+  onChange: (locale: SupportedLocale) => void;
+  /** Pass locale dicts to show a green dot indicator when content exists */
+  contentIndicators?: LocaleDict[];
+  className?: string;
+}
+
+/**
+ * Horizontal locale tab bar for the admin landing editor.
+ * Shows a green dot on tabs that have content filled in.
+ */
+export function LocaleTabs({
+  activeLocale,
+  onChange,
+  contentIndicators,
+  className,
+}: LocaleTabsProps) {
+  const { t } = useTranslation();
+
+  const hasContent = (locale: SupportedLocale): boolean => {
+    if (!contentIndicators || contentIndicators.length === 0) return false;
+    return contentIndicators.some((dict) => {
+      const value = dict[locale];
+      return typeof value === 'string' && value.trim().length > 0;
+    });
+  };
+
+  return (
+    <div className={cn('space-y-1', className)}>
+      <div className="flex items-center gap-1.5">
+        {SUPPORTED_LOCALES.map((locale) => {
+          const meta = LOCALE_META[locale];
+          const isActive = locale === activeLocale;
+          const filled = hasContent(locale);
+          const isRtl = meta.rtl;
+
+          return (
+            <button
+              key={locale}
+              type="button"
+              onClick={() => onChange(locale)}
+              dir={isRtl ? 'rtl' : 'ltr'}
+              className={cn(
+                'relative flex items-center gap-1.5 rounded-lg px-3 py-1.5 text-xs font-medium transition-all',
+                isActive
+                  ? 'bg-accent-500/15 text-accent-400 ring-1 ring-accent-500/30'
+                  : 'bg-dark-800/50 text-dark-400 hover:bg-dark-700/50 hover:text-dark-300',
+              )}
+              aria-label={`${t('admin.landings.localeTab')}: ${meta.name}`}
+              aria-pressed={isActive}
+            >
+              <span>{meta.flag}</span>
+              <span>{meta.name}</span>
+              {filled && !isActive && (
+                <span className="absolute -right-0.5 -top-0.5 h-2 w-2 rounded-full bg-success-500" />
+              )}
+            </button>
+          );
+        })}
+      </div>
+      <p className="text-xs text-dark-500">{t('admin.landings.localeHint')}</p>
+    </div>
+  );
+}

src/components/admin/LocalizedInput.tsx

@@ -0,0 +1,70 @@
+import { LOCALE_META, type LocaleDict, type SupportedLocale } from '../../api/landings';
+import { cn } from '../../lib/utils';
+
+interface LocalizedInputProps {
+  value: LocaleDict;
+  onChange: (value: LocaleDict) => void;
+  locale: SupportedLocale;
+  placeholder?: string;
+  multiline?: boolean;
+  rows?: number;
+  maxLength?: number;
+  id?: string;
+  className?: string;
+}
+
+/**
+ * An input (or textarea) that edits a single locale key within a LocaleDict.
+ * Shows `value[locale]` and updates the dict immutably on change.
+ */
+export function LocalizedInput({
+  value,
+  onChange,
+  locale,
+  placeholder,
+  multiline = false,
+  rows = 2,
+  maxLength,
+  id,
+  className,
+}: LocalizedInputProps) {
+  const currentValue = value[locale] ?? '';
+  const isRtl = LOCALE_META[locale].rtl;
+
+  const handleChange = (newText: string) => {
+    onChange({ ...value, [locale]: newText });
+  };
+
+  const inputClasses = cn(
+    'w-full rounded-lg border border-dark-700 bg-dark-800 px-3 py-2 text-sm text-dark-100 outline-none focus:border-accent-500',
+    className,
+  );
+
+  if (multiline) {
+    return (
+      <textarea
+        id={id}
+        dir={isRtl ? 'rtl' : 'ltr'}
+        value={currentValue}
+        onChange={(e) => handleChange(e.target.value)}
+        placeholder={placeholder}
+        rows={rows}
+        maxLength={maxLength}
+        className={inputClasses}
+      />
+    );
+  }
+
+  return (
+    <input
+      id={id}
+      type="text"
+      dir={isRtl ? 'rtl' : 'ltr'}
+      value={currentValue}
+      onChange={(e) => handleChange(e.target.value)}
+      placeholder={placeholder}
+      maxLength={maxLength}
+      className={inputClasses}
+    />
+  );
+}

src/components/admin/index.ts

@@ -12,6 +12,8 @@ export * from './FavoritesTab';
 export * from './SettingsTab';
 export * from './SettingsMobileTabs';
 export * from './SettingsSearch';
+export * from './LocaleTabs';
+export * from './LocalizedInput';
 
 // Constants and utils
 export * from './constants';