feat(dashboard): Hosts widget worst first, load against cores, one home per fact (#5251)

The Hosts — Overview widget opens with a verdict ("VDNT-Util01: CPU high."
or "All 3 hosts healthy."), then one row per host under one header: CPU,
memory, disk / and load. Rows sort by host_glance: a down monitor, a
reading past critical, a quiet agent, a warning, then the healthy. Load
reads "16.8 / 8 cores", graded per core as Settings → Thresholds intends
(cores counted from the per-core CPU sub-resources, as on the host page).
A quiet agent's last figures are shown uncoloured, with when it last reported.

Ping and 24h uptime are gone from this widget: they belong to Monitors. So
are the unlabelled CPU sparkline and the 30-day uptime query it no longer
needs.

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

tests/integration/test_metric_latest.py

@@ -98,6 +98,29 @@ def test_a_quiet_host_keeps_its_last_values_and_reads_stale_not_missing(app):
     assert "never-" + quiet not in overview          # no samples at all: absent
 
 
+
+def test_load_is_read_against_the_hosts_cores(app):
+    """#5251: cores are counted from the per-core CPU sub-resources, and load
+    per core is load_1m as a % of them, the figure "load" thresholds grade."""
+    from steward.core.alerts import record_metrics
+    from steward.hosts.service import agent_overview_by_host
+
+    now = datetime.now(timezone.utc)
+    host = "cores-" + uuid.uuid4().hex[:8]
+
+    async def go():
+        async with app.db_sessionmaker() as s:
+            async with s.begin():
+                await record_metrics(s, [
+                    _sample(host, "load_1m", 3.0, now),
+                    _sample(host + ":core0", "cpu_pct", 80.0, now),
+                    _sample(host + ":core1", "cpu_pct", 90.0, now),
+                ])
+            return await agent_overview_by_host(s, [host], 180)
+
+    h = asyncio.run(go())[host]
+    assert (h["cores"], h["load_per_core"]) == (2, 150)
+
 def test_retention_drops_a_latest_value_with_its_raw_history(app):
     from steward.core.alerts import record_metrics
     from steward.core.metrics_retention import rollup_plugin_metrics