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>

steward/ansible/executor.py

@@ -316,9 +316,13 @@ def build_extra_vars_file(merged: dict | None, tmpdir: str) -> tuple[list[str],
 
 
 def ansible_env(creds: dict | None, base_env) -> dict:
-    """Return a copy of base_env with ANSIBLE_HOST_KEY_CHECKING set from creds."""
+    """Return a copy of base_env with ANSIBLE_HOST_KEY_CHECKING set from creds,
+    and the interpreter found quietly (#5334): Ansible still discovers each
+    host's Python, but no longer warns about it on every run. A target or group
+    that sets ansible_python_interpreter still wins."""
     env = dict(base_env)
     env["ANSIBLE_HOST_KEY_CHECKING"] = "True" if (creds or {}).get("host_key_checking") else "False"
+    env.setdefault("ANSIBLE_PYTHON_INTERPRETER", "auto_silent")
     return env