feat: add cron job to remove orphan conversations (#13335)

## Description

This PR includes cron job to delete the orphans

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)

## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Introduces a scheduled cleanup for conversations missing `contact` or
`inbox`.
> 
> - Adds `Internal::RemoveOrphanConversationsService` to batch-delete
orphan conversations (scoped by optional `account`, within a
configurable `days` window) with progress logging
> - New `Internal::RemoveOrphanConversationsJob` that invokes the
service; scheduled via `config/schedule.yml` to run every 12 hours on
`housekeeping` queue
> - Refactors rake task `chatwoot:ops:cleanup_orphan_conversations` to
use the service and report `total_deleted` after confirmation
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
59a24715cc59f048d08db3f588cde6fa036f3166. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

config/schedule.yml

@@ -66,3 +66,10 @@ remove_old_notification_job:
   cron: '30 22 * * *'
   class: 'Notification::RemoveOldNotificationJob'
   queue: purgable
+
+# executed every 12 hours
+# to remove orphan conversations without contact
+remove_orphan_conversations_job:
+  cron: '0 */12 * * *'
+  class: 'Internal::RemoveOrphanConversationsJob'
+  queue: housekeeping