Agent Activity: stop paging a grid whose unit is hosts

[mastacontrola]

Follow-up to #1715, from testing it in a real browser. Three faults, one root.

Paging counts rows; this page's unit is hosts.

Expanding telliottwin11 (83 events) at 25 rows a page filled pages 1–3 with that host
and pushed every other host onto page 4 — and rowGroup redraws a group's header on every
page the group spans, so the host appeared four times, each apparently expanded:

page1: [telliottwin11]
page2: [telliottwin11]
page3: [telliottwin11]
page4: [telliottwin11, 7550precision, fogagent-vm, WS-014, ...]

That is not a rowGroup bug; it is what paging by row does when the grouped thing is
bigger than a page. And no page length fixes it, because the rows an expansion adds are
a property of the host, not of the setting.

So paging is off. Collapsed, the grid is one row per host; expanded, it gets longer
and you scroll. The seed is still bounded by MAX_HOSTS and each expansion by
ROWS_PER_HOST — this is not "no limit". Scroller is not the alternative:
registerTable() excludes any rowGroup table from it.

The empty "entries per page" box. With paging gone the length control has nothing to
put in itself and rendered as an empty box beside its own label — reported as unreadable
in both themes, which it was, because there was nothing in it to read. lengthChange: false removes the control instead of styling an empty one.

Refresh killed the expander. The toolbar's Refresh is dt.clear().draw() +
ajax.reload(), which throws the rows away and re-fetches the seed. The per-host maps
survived it, so a host still marked loaded was never re-fetched, its rows were gone,
and clicking its header did nothing. It read as the expander breaking permanently after
one press. They now reset on xhr.dt.

Verified on the live install

group headers, collapsed / expanded	21 / 21
duplicate headers when expanded	none
hosts displaced by an expansion	none
length control / pager present	0 / 0
expand after pressing Refresh	works (21 → 103 rows)

Checked in both themes.

Three more gates in tests/agent-activity-grouping.test.php (24 checks now), each
proven by reintroducing the defect and watching it go red. Both PHPStan passes clean,
unscoped; suite 335 passed, 1 failed — certificate-table.test.php, which fails
identically on an unmodified base checkout and is green in CI.

FOG_BCACHE_VER 363 → 364.

🤖 Generated with Claude Code

https://claude.ai/code/session_01JWJMQYE2br8E7Ehr55SJp2