feat(dashboard): an Alerts widget beside the Overview; the Overview's overflow links to Alerts and Monitors (#5510)

The Alerts widget (/alerts/widget) is shaped like every widget: a verdict
("2 firing, 1 silent." / "Nothing firing: all 12 rules are quiet."), then
what is firing or silent with its reading now, what the rule fires on and
since when, then what someone acknowledged and who; a line when alert
email failed in the last 7 days or is retrying (outbox.alert_trouble),
linking admins to Settings -> System; the quiet rules counted, a covering
rule once. It sits beside the Overview in the recommended layout (6x4
each).

The Overview's "+N more" line pointed at the removed /status/; alerts now
link to /alerts/ and monitors to /monitors/.

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

docs/core/alerting.md

@@ -232,6 +232,17 @@ host. Each channel's result shows under the button. Nothing fires, the rule's
 history doesn't change, and the test is recorded in the audit log as
 `alert_rule.tested`.
 
+### On the dashboard
+
+The **Alerts** widget (`/alerts/widget`) sits beside the Overview in the
+recommended layout. It opens with a verdict ("2 firing, 1 silent." or
+"Nothing firing: all 12 rules are quiet."). Below that it lists what is
+firing or silent: each rule, what it watches, its reading now against what
+it fires on, and since when. Acknowledged alerts follow, with who
+acknowledged them and when. A line appears when alert email has failed in
+the last 7 days or is still retrying, linking admins to Settings → System.
+The quiet rules are counted at the end.
+
 ---
 
 ## Data Models