fix: EmailManager route calls get_email_users not get_users

The method is named get_email_users in EmailManager; the route was
calling the non-existent get_users, causing an AttributeError on every
GET /api/email/users request.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_email_endpoints.py

@@ -39,7 +39,7 @@ class TestGetEmailUsers(unittest.TestCase):
 
     @patch('app.email_manager')
     def test_get_users_returns_200_with_list(self, mock_em):
-        mock_em.get_users.return_value = [
+        mock_em.get_email_users.return_value = [
             {'username': 'alice@cell', 'domain': 'cell'},
             {'username': 'bob@cell', 'domain': 'cell'},
         ]
@@ -51,14 +51,14 @@ class TestGetEmailUsers(unittest.TestCase):
 
     @patch('app.email_manager')
     def test_get_users_returns_empty_list_when_no_users(self, mock_em):
-        mock_em.get_users.return_value = []
+        mock_em.get_email_users.return_value = []
         r = self.client.get('/api/email/users')
         self.assertEqual(r.status_code, 200)
         self.assertEqual(json.loads(r.data), [])
 
     @patch('app.email_manager')
     def test_get_users_returns_500_on_exception(self, mock_em):
-        mock_em.get_users.side_effect = Exception('mailbox unreachable')
+        mock_em.get_email_users.side_effect = Exception('mailbox unreachable')
         r = self.client.get('/api/email/users')
         self.assertEqual(r.status_code, 500)
         self.assertIn('error', json.loads(r.data))