Fix TypeError when iterating storage keys

PHP converts numeric-looking string keys to integers when iterating arrays.
Cast keyId to string in listKeys() to handle this edge case.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: mowens3

src/ApiKey/ApiKeyManager.php

@@ -63,6 +63,8 @@ public function listKeys(): array
             if (!is_array($record)) {
                 continue;
             }
+            // Cast keyId to string in case PHP converted numeric-looking keys to int
+            $keyId = (string) $keyId;
             $keys[$keyId] = $this->recordToApiKey($keyId, $record);
         }