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/templates/ansible/inventory/group_detail.html

@@ -10,12 +10,14 @@
 {% set can_edit = session.user_role in ('operator', 'admin') %}
 {{ ansible_tabs("inventory") }}
 {{ page_header(group.name) }}
+{#- The name a play uses for it (#5334): Ansible takes only letters, digits and _. #}
 
 <p class="page-verdict">
   {%- set members = group.targets|sort(attribute='name') %}
   {%- if members %}{{ members|length }} member{{ 's' if members|length != 1 }}:
   {% for t in members %}<a href="/ansible/inventory/targets/{{ t.id }}">{{ t.name }}</a>{{ ", " if not loop.last }}{% endfor %}
   {%- else %}<span class="tone-warn">no members</span>{% endif %}
+  · plays call it <code>{{ ansible_name }}</code>
   {%- if used %} · scheduled by {% for s in used %}<a href="/ansible/schedules/{{ s.id }}">{{ s.name }}</a>{{ ", " if not loop.last }}{% endfor %}{% endif %}
 </p>