**Patch Plan**
- **File**: `store.py`
- **Function**: `get_user`
- **Edit**: Change `return USERS.get(email)` to `return USERS.get(email.strip().lower())`

**Regression Test**
```python
def test_login_normalization():
    USERS.clear()
    save_user("  User@Example.COM  ", "hash123")
    assert login("user@example.com", "hash123") is True
    assert login("  USER@EXAMPLE.COM  ", "hash123") is True
```