تطوير إطار اختبارات آلية لمشروع OrangeHRM باستخدام Playwright وPage Object Model

## Summary

This PR expands the OrangeHRM Playwright test suite by introducing **Page Object Model (POM)** classes for **Login** and **PIM/Add Employee**, plus a new **end-to-end “Add Employee”** test. It also improves test setup by adding a reusable **admin login fixture** and extending coverage for **invalid login credentials**.

## What changed

- **New POM pages**

- `pages/login_page.py`: login helpers (valid admin login + invalid credentials assertions)

- `pages/pim_page.py`: PIM navigation + “Add Employee” / “Employee List” tabs

- `pages/pim/add_employee_page.py`: “Add Employee” form interactions and save validation

- **Fixtures**

- `tests/conftest.py`: adds `login_with_admin` fixture (and keeps autouse `goto` navigation)

- **Tests**

- `tests/e2e/test_add_employee.py`: new E2E test that logs in and adds an employee

- `tests/e2e/test_example.py`: adds/organizes invalid-credential scenarios (including parametrized coverage)

## Test plan

- Run all tests:

pytest -q