[FSSDK-12670] Add comment explaining the < 2 identifiers guard

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jaeopt

lib/odp/odp_manager.ts

@@ -229,6 +229,8 @@ export class DefaultOdpManager extends BaseService implements OdpManager {
       identifiers.set(ODP_USER_KEY.FS_USER_ID, finalUserId);
     }
 
+    // Identify requires 2+ identifiers to link (e.g., vuid + fs_user_id).
+    // A single identifier has no cross-reference value and generates unnecessary traffic.
     if (identifiers.size < 2) {
       this.logger.log(LogLevel.Debug, 'ODP identify event is not dispatched (fewer than 2 valid identifiers).');
       return;