**Patch Plan**
Centralize email normalization in the lookup function so dictionary key matching is consistent with storage.

**Exact File/Function Edits**
- `store.py` → `get_user(email)`:
  ```python
  # Before
  return USERS.get(email)
  # After
  return USERS.get(email.strip().lower())
  ```

**Regression Test**
```python
def test_login_email_normalization():
    from store import save_user
    from routes import login

    save_user("  Admin@Site.COM  ", "secure_hash")
    assert login("admin@site.com", "secure_hash") is True
    assert login("  ADMIN@SITE.COM  ", "secure_hash") is True
```