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>

steward/alerts/routes.py

@@ -178,6 +178,19 @@ async def active_fragment():
         rules_off=sum(1 for r in rules if not r.enabled))
 
 
+@alerts_bp.get("/widget")
+@require_role(UserRole.viewer)
+async def widget():
+    """The dashboard Alerts widget (#5510): a verdict, what is firing or
+    silent, then what someone has taken, a line when alert email is failing,
+    and the quiet rules counted."""
+    async with current_app.db_sessionmaker() as db:
+        active = await alert_svc.active_rows(db, datetime.now(timezone.utc))
+        view = alert_svc.widget_view(active, await alert_svc.list_rules(db))
+        email = await outbox.alert_trouble(db)
+    return await render_template("alerts/widget.html", **view, email=email)
+
+
 def _delivery(label: str, sent: bool | None, error: str | None) -> dict | None:
     """A channel's outcome as recorded on the event; None when not tried."""
     if sent is None: