fix: Preserve sub-namespace when generating Entity from Model (--return=entity)

[xgrind]

This change ensures that when a model is generated with --return=entity,
the Entity generator is invoked with the fully-qualified entity class name
so any sub-namespace in the model name (for example Admin) is preserved
in the Entity file and namespace.

How to reproduce (before fix)

1. Run: php spark make:model Admin/Class --return entity
2. Model is created under app/Models/Admin/Class.php
3. Entity is created under app/Entities/Class.php (missing Admin namespace)

How to verify (after applying fix)

1. Run: php spark make:model Admin/Class --return entity
2. Model: app/Models/Admin/Class.php
3. Entity: app/Entities/Admin/Class.php (namespace App\Entities\Admin)

[mergeable]

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