fix(theming): use fully-qualified \OCP\IConfig in Server.php DI

IConfig has no use-import in Server.php; the rest of the file uses
\OCP\IConfig::class directly.

Signed-off-by: Anna Larch <anna@nextcloud.com>
AI-Assisted-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: miaulalala

lib/private/Server.php

@@ -1031,7 +1031,7 @@ public function __construct($webRoot, \OC\Config $config) {
 					$c->get(ITempManager::class),
 					$backgroundService,
 					new AppConfig(
-						$c->get(IConfig::class),
+						$c->get(\OCP\IConfig::class),
 						$c->get(IAppConfig::class),
 						'theming',
 					),