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/_macros.html

@@ -84,3 +84,20 @@
   {%- if kwargs.get('confirm') %} data-confirm="{{ kwargs.confirm }}"{% endif %}>{{ icon }}</button>
 {%- endif -%}
 {%- endmacro %}
+
+{# A list that continues itself (#5211, pref 172; static/scroll-more.js).
+   scroll_more ends a page while there are more rows: it fetches `url` (the
+   next page, built with core.paging's cursor) when it comes near the
+   viewport, and is replaced by that page's rows. scroll_end ends the last
+   page. Pass `cols` inside a table body, to render as a full-width row. #}
+{% macro scroll_more(url, cols=none) -%}
+{%- if cols %}<tr data-scroll-more hx-get="{{ url }}" hx-trigger="scroll-more" hx-swap="outerHTML"><td colspan="{{ cols }}">
+{%- else %}<div data-scroll-more hx-get="{{ url }}" hx-trigger="scroll-more" hx-swap="outerHTML">{% endif -%}
+<span class="field-hint" role="status" aria-live="polite" data-scroll-status>Loading more…</span>
+{%- if cols %}</td></tr>{% else %}</div>{% endif %}
+{%- endmacro %}
+
+{% macro scroll_end(cols=none, text="End of the list.") -%}
+{%- if cols %}<tr><td colspan="{{ cols }}"><span class="field-hint" role="status">{{ text }}</span></td></tr>
+{%- else %}<p class="field-hint" role="status">{{ text }}</p>{% endif %}
+{%- endmacro %}