Connect License class to the real auroraplugins.com license server

- License.php now calls the aurora-licensing plugin's REST API
  (/wp-json/aurora-licensing/v1/validate|activate|deactivate) instead of
  treating any non-empty license_key as active. Result is cached in the
  aurora_admin_license_status option for 12 hours; is_active() and
  is_feature_available() read the cache instead of hitting the network on
  every admin page load.
- Hooks update_option_aurora_admin_settings to activate/deactivate
  immediately when the license_key setting actually changes, rather than
  waiting out the cache. Instantiated in AuroraAdmin.php so that hook
  registers.
- Settings page now surfaces the real status (active/invalid/unreachable,
  with the server's own message) as a status line under the License key
  field, instead of a field that silently does nothing.
- Verified live against the real server: a fake test key correctly came
  back locked with the server's own "License key not found." message.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

admin/src/App/AuroraAdmin.php

@@ -2,6 +2,7 @@
 namespace AuroraAdmin\App;
 
 use AuroraAdmin\Options\Settings;
+use AuroraAdmin\Licensing\License;
 use AuroraAdmin\Shell\Shell;
 use AuroraAdmin\Pages\DashboardTakeover;
 use AuroraAdmin\Pages\SettingsPage;
@@ -35,6 +36,7 @@ class AuroraAdmin
   public function __construct()
   {
     new Settings();
+    new License();
     new Shell();
     new DashboardTakeover();
     new SettingsPage();