feat: identify accounts by a uuid in the oauth2 sub claim

src/Controller/Api/UserinfoController.php

@@ -58,7 +58,11 @@ class UserinfoController extends AbstractController
             // addresses on a person's record as a login and answers all of them with the same
             // ids and the same first contact address, so only the local account tells the staff
             // account and the private one apart — and they hold different roles.
-            $data->subject = (string) $user->getId();
+            //
+            // The uuid, not the primary key: consumers store this value and match their own
+            // accounts on it, so it must not disclose how many accounts exist or let one
+            // account's identifier be guessed from another's.
+            $data->subject = $user->getUuid();
             $data->loginEmail = $user->getEmail();
 
             // Patch current user's roles. The implicit ROLE_USER says nothing about the