# Set Library Visibility

Set library visibility for a specific user (Admin only).

**Endpoint**: `POST /api/libraries/visibility`
**Auth**: Required (Admin only)
**Content-Type**: `application/json`

## Request Body

| Field      | Type    | Required | Description                        |
| ---------- | ------- | -------- | ---------------------------------- |
| user_id    | string  | Yes      | User UUID                          |
| library_id | string  | Yes      | Library UUID                       |
| is_visible | boolean | Yes      | Whether library is visible to user |

### Example Request

```json
{
  "user_id": "user-uuid",
  "library_id": "library-uuid",
  "is_visible": true
}
```

## Response (200 OK)

```json
{
  "user_id": "user-uuid",
  "library_id": "library-uuid",
  "is_visible": true
}
```

## Error Responses

| Code | Description               |
| ---- | ------------------------- |
| 400  | Invalid input data        |
| 401  | Invalid or expired token  |
| 403  | User is not an admin      |
| 404  | User or library not found |
