fix(admin): show flag for every country code, not just hardcoded 25-36

User reported the EE (Estonia) flag rendered as plain text 'EE' on the
admin servers page. Root cause: getCountryFlag() in AdminServers.tsx
and AdminServerEdit.tsx hardcoded a 25-entry codeMap that didn't
include EE; falling through to 'return code' produced raw text.

Two other admin pages (AdminRemnawaveSquadDetail, AdminUserDetail)
had bigger 35-entry maps that did include EE — so EE worked there
but MX/AR/EG/ZA and friends still wouldn't. AdminRemnawave repeated
the same 35-entry map. AdminTrafficUsage already had the correct
algorithmic ISO→regional-indicator code but as a local duplicate of
utils/subscriptionHelpers.

Unify all six on the single algorithmic helper:

- getFlagEmoji() in utils/subscriptionHelpers.ts now:
  * accepts string | null | undefined (callers don't need to guard)
  * trims whitespace
  * validates [A-Za-z]{2} before composing regional indicators
- Each admin page now either imports getFlagEmoji directly or wraps
  it with the page's preferred fallback character (e.g. '🌍' for
  empty codes where the UI expects a placeholder).

src/pages/AdminTrafficUsage.tsx

@@ -18,6 +18,7 @@ import {
   type TrafficEnrichmentData,
 } from '../api/adminTraffic';
 import { usePlatform } from '../platform/hooks/usePlatform';
+import { getFlagEmoji as _sharedGetFlagEmoji } from '../utils/subscriptionHelpers';
 
 // ============ TanStack Table module augmentation ============
 
@@ -40,14 +41,9 @@ const formatBytes = (bytes: number): string => {
   return parseFloat((bytes / Math.pow(k, i)).toFixed(2)) + ' ' + sizes[i];
 };
 
-const getFlagEmoji = (countryCode: string): string => {
-  if (!countryCode || countryCode.length !== 2) return '';
-  const codePoints = countryCode
-    .toUpperCase()
-    .split('')
-    .map((char) => 127397 + char.charCodeAt(0));
-  return String.fromCodePoint(...codePoints);
-};
+// Локальная обёртка над общим helper'ом, чтобы внутренние сигнатуры (string)
+// оставались как были и call-sites не меняли.
+const getFlagEmoji = (countryCode: string): string => _sharedGetFlagEmoji(countryCode);
 
 const formatCurrency = (kopeks: number): string => {
   const rubles = kopeks / 100;