✨ Add maintenance task to remove unredeemed vouchers of deleted users

[0x46616c6b]

Summary

• Add a scheduled maintenance task that removes unredeemed vouchers belonging to soft-deleted users as a safety-net
• The task runs weekly at 05:00 via the maintenance scheduler and can be triggered manually from the admin maintenance page
• While DeleteHandler::deleteUser() already cleans up unredeemed vouchers synchronously during deletion, this task catches any that may have been missed (e.g. race conditions, manual DB changes)

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_{The changes and the PR were generated by OpenCode.}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
1 Accepted issue

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[y3n4]

Feels like a lot of new code when a database migration should also do the job, at least for existing remnants, IMO.

If we assume that race conditions can lead to a voucher not being deleted, I would rather try to fix/harden the delete handler.

Don't want to stand in your way though.

[0x46616c6b]

Feels like a lot of new code when a database migration should also do the job, at least for existing remnants, IMO.

If we assume that race conditions can lead to a voucher not being deleted, I would rather try to fix/harden the delete handler.

Don't want to stand in your way though.

It's about 70 lines of code (not including tests), which I think is okay. In comparison, a migration also requires a few lines of code and is a one-shot.