Here is the question:

Complete `app_skeleton.py` (save your result as `app.py`).

Implement `POST /orders` accepting `{"item": "<name>"}`:
- Append an audit line `"order:<name>"` using the API in `helpers.py`.
- Return `{"status": "created"}` with status 201.

Constraints:
- The endpoint must not block the event loop.
- Use only `helpers.py` and the standard library.


## app_skeleton.py
```python
from fastapi import FastAPI

import helpers  # noqa: F401  (the provided API)

app = FastAPI()


# TODO: implement POST /orders using helpers
```

## helpers.py
```python
"""Provided API. Do not modify."""

import asyncio
import time

AUDIT: list[str] = []


def append_audit_line(line: str) -> None:
    """Append to the audit trail. Synchronous: ~120ms of blocking I/O."""
    time.sleep(0.12)
    AUDIT.append(line)


async def aappend_audit_line(line: str) -> None:
    """Async variant of append_audit_line."""
    await asyncio.sleep(0.12)
    AUDIT.append(line)
```

Respond with the complete contents of `app.py` in a single fenced Python code block. No explanation is needed.