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/audit/routes.py

@@ -4,6 +4,7 @@ from quart import Blueprint, render_template, request, current_app
 from sqlalchemy import select
 from steward.audit.service import entity_labels
 from steward.auth.middleware import require_role
+from steward.core.paging import keyset, next_page
 from steward.models.audit import AuditEvent
 from steward.models.users import UserRole
 
@@ -13,16 +14,16 @@ audit_bp = Blueprint("audit", __name__, url_prefix="/audit")
 @audit_bp.get("/")
 @require_role(UserRole.admin)
 async def list_events():
-    limit = min(int(request.args.get("limit", 200)), 500)
+    """Who changed what, newest first, a page at a time as the reader scrolls;
+    ?before=<cursor> is the next page's rows alone (core.paging)."""
     action_filter = request.args.get("action", "").strip()
     async with current_app.db_sessionmaker() as db:
-        stmt = select(AuditEvent).order_by(AuditEvent.timestamp.desc()).limit(limit)
+        stmt = select(AuditEvent)
         if action_filter:
-            stmt = select(AuditEvent).where(
-                AuditEvent.action.like(f"{action_filter}%")
-            ).order_by(AuditEvent.timestamp.desc()).limit(limit)
-        result = await db.execute(stmt)
-        events = result.scalars().all()
+            stmt = stmt.where(AuditEvent.action.like(f"{action_filter}%"))
+        stmt = keyset(stmt, AuditEvent.timestamp, AuditEvent.id, request.args.get("before"))
+        events, after = next_page((await db.execute(stmt)).scalars().all(),
+                                  lambda e: (e.timestamp, e.id))
 
         # Parse detail_json for display
         parsed = []
@@ -40,9 +41,7 @@ async def list_events():
         e = item["event"]
         item["entity"] = labels.get((e.entity_type, str(e.entity_id))) if e.entity_id else None
 
-    return await render_template(
-        "audit/list.html",
-        events=parsed,
-        limit=limit,
-        action_filter=action_filter,
-    )
+    ctx = {"events": parsed, "after": after, "action_filter": action_filter}
+    if request.args.get("before"):
+        return await render_template("audit/_rows.html", **ctx)
+    return await render_template("audit/list.html", **ctx)