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>

tests/core/test_ansible_runs_page.py

@@ -50,7 +50,7 @@ async def test_the_runs_list_names_each_run_with_one_badge(app):
     )]
     async with app.test_request_context("/ansible/"):
         session["user_role"] = "viewer"
-        page = await render_template("ansible/index.html", runs=runs)
+        page = await render_template("ansible/index.html", runs=runs, after="2026-10-07T01:00:00+00:00|x")
 
     main = page[page.index("<main"):]
     assert '<a href="/ansible/runs/aaaa1111" title="steward:target:t1">update.yml on web-1</a>' in main
@@ -58,6 +58,8 @@ async def test_the_runs_list_names_each_run_with_one_badge(app):
     assert '<span class="badge badge-info">Running</span>' in main
     assert '<span class="badge badge-crit">Failed</span>' in main
     assert '<span class="badge badge-ok">Succeeded</span>' in main
+    # The list continues itself as the reader scrolls (#5211): no cap of 50.
+    assert 'data-scroll-more hx-get="/ansible/?before=2026-10-07T01%3A00%3A00%2B00%3A00%7Cx"' in main
     assert "2m 5s" in main and "40s" in main and " so far" in main
     assert "dry run" in main and "ago" in main
     assert "RUNNING" not in main and "FAILED" not in main  # the old shouted status text is gone