fix: correct Account Center enablement — mfa field is a string enum

Logto's PATCH /api/account-center expects mfa as 'Off'|'ReadOnly'|'Edit',
not a nested object. Fixes 400 Bad Request on startup.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/main/java/net/siegeln/cameleer/saas/identity/LogtoManagementClient.java

@@ -664,7 +664,7 @@ public class LogtoManagementClient {
                 .body(Map.of(
                         "enabled", true,
                         "fields", Map.of(
-                                "mfa", Map.of("edit", "ReadonlyProfile")
+                                "mfa", "Edit"
                         )
                 ))
                 .retrieve()