fix: guard allowedRoles() against corrupt filtered results

The lit_mcp_allowed_roles filter could return a non-array, causing
array_filter() to throw TypeError in PHP 8.1+. Now fallback to
['administrator'] if filter result is not an array.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

src/Access.php

@@ -46,6 +46,9 @@ final class Access
         }
 
         $roles = apply_filters('lit_mcp_allowed_roles', $roles);
+        if (! is_array($roles)) {
+            $roles = self::DEFAULT_ROLES;
+        }
 
         return array_values(array_filter($roles, 'is_string'));
     }