fix(ansible): group names Ansible accepts, and interpreter discovery without the warning (#5334)

Every run warned twice because of Steward's own inventory:
- 'Invalid characters were found in group names': the group 'Docker
  Swarm' went into the inventory as typed. ansible_group_name() cleans it
  to docker_swarm (lower case, [a-z0-9_], never a leading digit); two
  names that clean alike get _2, _3 so neither folds into the other. The
  group page says what plays call it. The display name is unchanged.
- Python interpreter discovery: ansible_env sets
  ANSIBLE_PYTHON_INTERPRETER=auto_silent unless the environment already
  sets one; a target or group's ansible_python_interpreter still wins.

Runs are scoped by target set (steward:group:<id>), not by group name,
and --limit is free text, so neither path depends on the name.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_ansible_credentials.py

@@ -49,6 +49,10 @@ def test_ansible_env_host_key_checking_toggle():
     assert ansible_env({"host_key_checking": True}, {})["ANSIBLE_HOST_KEY_CHECKING"] == "True"
     assert ansible_env({"host_key_checking": False}, {})["ANSIBLE_HOST_KEY_CHECKING"] == "False"
     assert ansible_env({}, {})["ANSIBLE_HOST_KEY_CHECKING"] == "False"
+    # Interpreter discovery stays, without its warning on every run (#5334);
+    # an interpreter set in the environment is left as it is.
+    assert ansible_env({}, {})["ANSIBLE_PYTHON_INTERPRETER"] == "auto_silent"
+    assert ansible_env({}, {"ANSIBLE_PYTHON_INTERPRETER": "/usr/bin/python3"})["ANSIBLE_PYTHON_INTERPRETER"] == "/usr/bin/python3"
     assert ansible_env(None, {})["ANSIBLE_HOST_KEY_CHECKING"] == "False"