### Preview a plan change for many subscribers

`POST /api/v1/users/bulk-change-profile/preview`

Read-only. Takes the same body as bulk-change-profile and reports each subscriber's current plan, and which rows the change would refuse.

- Authentication: manager session (JWT) or API token
- Permission: `prm_users_change_profile` (Change user profile)
- Risk: write
- Rate limit bucket: `t_mutate`

#### Response — 200 OK

```json
{
  "data": {
    "rows": [
      { "id": 4711, "username": "ahmed", "current_profile_id": 5, "current_profile_name": "Home-10M" },
      { "id": 4712, "username": "mona", "current_profile_id": 12, "current_profile_name": "Home-20M",
        "blocked": true, "reason": "same_profile", "message": "Already on this plan." }
    ],
    "changing": 1,
    "blocked": 1
  }
}
```