# 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 |
