test(alerts): seed metrics the way ingest does, through record_metrics (#5473)

#5473 "Opening an alert rule takes up to 15 s". With the rule pickers now
reading plugin_metric_latest, nine integration tests failed on rule_fields:
"host_agent has no resource 'box-…'". They seeded a resource by adding a raw
PluginMetric row, which no production path does: host-agent ingest and
record_metric both go through record_metrics, which keeps the latest-value
table. The seeds now go through record_metrics too.

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

tests/integration/test_alert_no_data.py

@@ -45,9 +45,9 @@ def test_silence_is_marked_once_and_cleared_by_data(app):
                 user = User(username=f"nd-{tag}", email=f"nd-{tag}@test", password_hash="x",
                             role=UserRole.admin)
                 s.add(user)
-                s.add(PluginMetric(source_module="host_agent", resource_name=res,
-                                   metric_name="cpu_pct", value=1.0,
-                                   recorded_at=now - timedelta(hours=1)))
+                await alerts.record_metrics(s, [PluginMetric(
+                    source_module="host_agent", resource_name=res, metric_name="cpu_pct",
+                    value=1.0, recorded_at=now - timedelta(hours=1))])
                 await s.flush()
                 ids = {}
                 for key, notify in (("loud", True), ("hushed", False)):
@@ -156,9 +156,9 @@ def test_a_series_quiet_only_while_steward_was_down_is_not_silent(app):
                 user = User(username=f"bk-{tag}", email=f"bk-{tag}@test", password_hash="x",
                             role=UserRole.admin)
                 s.add(user)
-                s.add(PluginMetric(source_module="host_agent", resource_name=res,
-                                   metric_name="cpu_pct", value=1.0,
-                                   recorded_at=now - timedelta(minutes=18)))
+                await alerts.record_metrics(s, [PluginMetric(
+                    source_module="host_agent", resource_name=res, metric_name="cpu_pct",
+                    value=1.0, recorded_at=now - timedelta(minutes=18))])
                 await s.flush()
                 fields = await alert_svc.rule_fields(
                     s, name=f"back {tag}", source_module="host_agent", resource_name=res,