feat(anomalies): a metric out of its normal is an anomaly to review (#5740)

#5740 "A metric that departs from its normal is recorded as an anomaly to
review, and is findable after it ends", milestone 513.

- Every minute each learned key's last 15 minutes is judged against its
  hour's normal: above the usual hold x1.25 and by the metric's floor opens
  an occurrence, which ends when the level comes back.
- metric_anomalies holds one row per item to review; a repeat while it
  still waits joins it as an occurrence (metric_anomaly_spans).
- An ended row nobody reviews within anomalies.review_days (14, Settings ->
  Thresholds) lapses; an ongoing one never does.
- Learning skips every hour an occurrence covers unless its anomaly was
  marked normal: no normal is learned without review.
- Alerts -> Anomalies lists those to review first, then the reviewed and
  lapsed under day dividers; marking is operator/admin and audited.
- The Overview widget and get_overview warn of open ones and count those
  to review; the host page shows its own; the weekly report lists the
  week's and the lapsed; MCP list_anomalies and review_anomaly.
- Reviewed and lapsed rows are pruned at data.retention_days, and kept
  in backups like alert history.

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

steward/alerts/service.py

@@ -104,13 +104,17 @@ PLUGIN_PAGES = {"traefik": "/plugins/traefik/", "unifi": "/plugins/unifi/",
 
 
 async def resource_url(db, rule: AlertRule) -> str | None:
-    """Where the thing a rule watches is shown, or None when nothing shows it.
+    """Where the thing a rule watches is shown, or None when nothing shows it."""
+    return await resource_url_for(db, rule.source_module, rule.resource_name)
+
+
+async def resource_url_for(db, source: str, resource: str) -> str | None:
+    """Where a (source, resource) of the metric store is shown, or None.
 
     host_agent resources are the host's name, or "<host>:<mount|nic|core>";
     docker's are "<host>/<container>"; a monitor's is its name under its type.
     """
     from steward.models.hosts import Host
-    source, resource = rule.source_module, rule.resource_name
     if source == "host_agent":
         name = resource.split(":", 1)[0]
         host_id = (await db.execute(