### Patch Plan

**1. `store.py`**
Update `get_user` to normalize the input email before lookup to match the logic in `save_user`.

```python
def get_user(email):
    return USERS.get(email.strip().lower())
```

**2. Regression Test**
Verify that users can log in regardless of leading/trailing whitespace or casing used during registration.

```python
def test_login_normalization():
    save_user("  User@Example.com  ", "hash123")
    # Should succeed despite different casing and whitespace
    assert login("User@Example.com", "hash123") is True
```