fix(ui): section tabs above the breadcrumb, so the Ansible tab strip holds still (#5214)

The tabs were drawn in each page's content block, which base.html renders
after the breadcrumb, so on every nested Ansible page the strip moved down a
line. base.html now has a section_tabs block above the breadcrumb, and every
Ansible page fills it. A guard in test_breadcrumbs.py fails any page that calls
a tabs macro outside that block.

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

steward/templates/ansible/schedule.html

@@ -7,9 +7,9 @@
 {% from "ansible/_macros.html" import interval_words %}
 {% block title %}{{ editing.name if editing else "New schedule" }} — Steward{% endblock %}
 {% block breadcrumb %}{{ crumbs([("Ansible", "/ansible/"), ("Schedules", "/ansible/schedules"), (editing.name if editing else "New schedule", "")]) }}{% endblock %}
+{% block section_tabs %}{{ ansible_tabs("schedules") }}{% endblock %}
 {% block content %}
 {% set can_edit = session.user_role in ('operator', 'admin') %}
-{{ ansible_tabs("schedules") }}
 {% call page_header(editing.name if editing else "New schedule") %}
     {% if editing and can_edit %}
     <form method="post" action="/ansible/schedules/{{ editing.id }}/run-now">{{ csrf_field() }}