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/_macros.html

@@ -73,9 +73,10 @@
 </div>
 {%- endmacro %}
 
-{# A section's own pages as tabs under the crumbs (#5328): items are
-   (key, label, href); the one whose key is `active` is the current page.
-   Links, not a tablist: each tab is its own page. #}
+{# A section's own pages as tabs (#5328): items are (key, label, href); the
+   one whose key is `active` is the current page. Links, not a tablist: each
+   tab is its own page. Call it in base.html's section_tabs block, which sits
+   above the breadcrumb, so the strip stays put as the trail grows. #}
 {% macro section_tabs(items, active, label) -%}
 <nav class="section-tabs" aria-label="{{ label }}">
   {%- for key, text, href in items %}