Migrate Drush commands to Drush 13 PSR-4 autodiscovery

Problem/Motivation

The ymca_sync module registers its Drush command class via drush.services.yml using the legacy Drush 8/9 service-tag ({ name: drush.command }) pattern. Drush 13 dropped support for this discovery mechanism, causing all yn-sync:* commands to silently disappear from drush list.

Proposed resolution

Migrate the command class to the Drush 13 PSR-4 autodiscovery standard as per the official Drush documentation on auto-discovered commands.

Remaining tasks

TBD

User interface changes

None.

API changes

None. All command names and aliases are unchanged: yn-sync:sync (yn-sync), yn-sync:list (yn-sync-list), yn-sync:enable (yn-sync:en), yn-sync:disable (yn-sync:dis).

Data model changes

None.