删除所有 Core Data 数据

```swift

let entities = PersistenceController.shared.container.managedObjectModel.entities
for entity in entities {
if ((entity.name) != nil) {
let deleteFetch = NSFetchRequest(entityName: entity.name!)
let deleteRequest = NSBatchDeleteRequest(fetchRequest: deleteFetch)

do {
try viewContext.execute(deleteRequest)
try viewContext.save()
} catch {
print ("There was an error")
}
}
}
```

Start with the provided Swift snippet and trace PersistenceController.shared, managedObjectModel, and viewContext in the repository. Clarify where this behavior should live and what “delete all Core Data data” should cover; done means the agreed deletion behavior is implemented and verified against the project’s existing usage.

Written by the indexing model from the issue text.