feat(ui): audit log, alert history and Ansible runs load as you scroll (#5211)

#5211 "Lists load as you scroll: audit, alert history, Ansible runs"
(milestone 477), per preference 172.

- core/paging.py: keyset paging over (time, id), newest first, with an
  opaque "<iso>|<id>" cursor; a page reads one row past itself to know
  whether another follows. No OFFSET, so rows added while someone scrolls
  never shift the pages after them.
- _macros.html scroll_more / scroll_end and static/scroll-more.js, written
  once: an IntersectionObserver with a 600px margin fetches the next page
  before the reader reaches the end; "Loading more…" while in flight,
  "End of the list." at the end, and a failed page says so with a Retry
  button instead of re-firing on every scroll.
- Audit log: no "Load more" link and no 500-row cap.
- Alert history: no 200-row stop with "pick a shorter range";
  alert_svc.history takes the cursor, so the MCP tool and the page share
  one query.
- Ansible runs: no silent cap of 50.

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

steward/templates/base.html

@@ -27,6 +27,7 @@
     <link rel="stylesheet" href="{{ url_for('static', filename='theme.css') }}">
     <link rel="stylesheet" href="{{ url_for('static', filename='steward.css') }}">
     <script src="{{ url_for('static', filename='chart-colors.js') }}"></script>
+    <script src="{{ url_for('static', filename='scroll-more.js') }}" defer></script>
     {% block head %}{% endblock %}
 </head>
 <body>