feat: enhance header context handling and add login page test

- Updated `header.html` to use `with` block for `active` context variable fallback
- Added test to verify login page renders correctly without `active` context

users/tests.py

@@ -12,6 +12,12 @@ User = get_user_model()
 
 @override_settings(EMAIL_BACKEND="django.core.mail.backends.locmem.EmailBackend")
 class UserAuthFlowTests(TestCase):
+    def test_login_page_renders_without_active_context(self):
+        response = self.client.get(reverse("users:login"))
+
+        self.assertEqual(response.status_code, 200)
+        self.assertTemplateUsed(response, "users/login.html")
+
     def test_registration_creates_inactive_user_and_sends_activation_email(self):
         response = self.client.post(
             reverse("users:register"),