feat(email): delivery you can see: each alert's email in history, outgoing email on Settings -> System (#5509)

#5509 "Delivery you can see: each alert's email state in history, and
outgoing email on Settings -> System" (milestone 501).

- Alerts -> History: an alert's email reads from the outbox (#5506):
  "gathering" with when it sends, "sending", "retrying" with the attempt,
  next try and the server's last answer, "sent", or "failed" naming each
  reader it didn't reach and why (outbox.delivery / email_states). Events
  from before the outbox keep what they recorded. The Notified column
  shows once an alert has a queued email.
- Settings -> System gets "Outgoing email": every email of the last 7
  days not yet sent, failures first, then the longest retrying, with
  recipient, kind, state and last error, and a count of what was sent.
  Failures and anything still retrying after 5 minutes lead the page's
  verdict (outbox.outgoing).
- get_alert_history (MCP) adds `email`: the same delivery state.

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

steward/mcp/tools/alerts.py

@@ -6,6 +6,7 @@ from datetime import datetime, timedelta, timezone
 from sqlalchemy import select
 
 from steward.alerts import service as alert_svc
+from steward.core import outbox
 from steward.mcp._context import current_caller, mcp_app
 from steward.models.alerts import AlertOperator, AlertRule, AlertState, MaintenanceWindow
 from steward.models.users import UserRole
@@ -82,7 +83,11 @@ async def get_alert_history(rule: str = "", range: str = "7d", limit: int = 50)
 
     Each transition carries the metric value that caused it and whether the
     email/webhook notification went out (with the error if not), plus the id
-    of any Ansible run the rule's action triggered. `by` names the person who
+    of any Ansible run the rule's action triggered. `email` is the email's
+    delivery: state "held" (gathering other alerts; `at` is when it sends),
+    "sending", "retrying" (`attempts`, next try `at`, last `error`), "sent"
+    or "failed" (`error` names each reader not reached); null when no email
+    was queued for it. `by` names the person who
     made it happen (an acknowledgement, or a rule edit that reset the alert);
     null when a reading or Steward itself did.
     """
@@ -93,6 +98,7 @@ async def get_alert_history(rule: str = "", range: str = "7d", limit: int = 50)
         chosen = pick(rule, rules, kind="alert rule", list_tool="list_alert_rules") if rule else None
         rows = await alert_svc.history(db, since, chosen.id if chosen else None, limit)
         names = await alert_svc.usernames(db, (e.actor_id for e, _ in rows))
+        emails = await outbox.email_states(db, [e.id for e, _ in rows])
     events = [
         {
             "rule_id": r.id,
@@ -106,6 +112,7 @@ async def get_alert_history(rule: str = "", range: str = "7d", limit: int = 50)
             "age_s": age_s(e.transitioned_at),
             "email_sent": e.email_sent,
             "email_error": e.email_error,
+            "email": ({**emails[e.id], "at": iso(emails[e.id]["at"])} if e.id in emails else None),
             "webhook_sent": e.webhook_sent,
             "webhook_error": e.webhook_error,
             "ansible_run_id": e.ansible_run_id,