Permanently delete an item

Hard-deletes the item — irreversible. Removes the item row, all edges with this item as source or target, the metadata row, every extension scoped to this item, and attachment references. Blob bytes themselves are content-addressed and may be retained if referenced by other items. Admin-only; the normal DELETE /items/{id} is the soft-delete-via-trash path most clients want. See Lifecycle — hard deletion.