refactor(i18n): drop the global $language, provide it from the controller layer

$language was a bootstrap-set global (literally Translator::class) that
reached views through four separate bridges: the BaseAdminController
extract whitelist, admin/functions.php, and the renderUnifiedLayoutHeader/
Footer $GLOBALS pulls. Removing the global and sourcing $language where
each page is actually assembled makes the dependency explicit.

- BaseAdminController::render() sets $data['language'] = Translator::class,
  covering every admin/reseller page it renders.
- renderUnifiedLayoutHeader()/Footer() and admin/functions.php set a local
  $language for the legacy header/footer and the standalone login/setup/post
  pages; the reseller login/post controllers set their own local.
- Non-view code (TableController, SearchAjaxController, Admin/Reseller
  ScopeBootstrap) calls Translator::get()/setLanguage() directly instead of
  through `global $language`.
- bootstrap.php no longer creates the $language global; initTranslator()
  and $allowedLangs call Translator:: directly.

Views keep their `$language::get(...)` syntax unchanged; $language is now a
local in every scope that renders one.

src/bootstrap.php

@@ -526,8 +526,7 @@ class XC_Bootstrap {
      * Initialize Translator (i18n).
      */
     private static function initTranslator(): void {
-        $language = Translator::class;
-        $language::init(MAIN_HOME . 'resources/langs/');
+        Translator::init(MAIN_HOME . 'resources/langs/');
     }
 
     /**
@@ -665,7 +664,7 @@ class XC_Bootstrap {
     private static function initAdminGlobals(): void {
         global $rDetect, $rMobile, $rTimeout, $rSQLTimeout, $rProtocol,
             $allServers, $rServers, $rSettings, $rProxyServers,
-            $rPermissions, $language, $allowedLangs;
+            $rPermissions, $allowedLangs;
 
         if (!defined('SERVER_ID')) {
             define('SERVER_ID', intval(ConfigReader::get('server_id')));
@@ -690,8 +689,7 @@ class XC_Bootstrap {
         }
         $rProxyServers = ServerRepository::getProxySimple($rPermissions);
 
-        $language     = Translator::class;
-        $allowedLangs = $language::available();
+        $allowedLangs = Translator::available();
 
         // Sort servers by order
         if (is_array($rServers)) {