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/alerts/episodes.py

@@ -87,8 +87,8 @@ def episodes(rows: list[dict], *, newest_page: bool, now: datetime, since: datet
         seen, deliveries = set(), []
         for s in steps:
             for d in s["deliveries"]:
-                if (d[0], d[1]) not in seen:
-                    seen.add((d[0], d[1]))
+                if (d["label"], d["state"]) not in seen:
+                    seen.add((d["label"], d["state"]))
                     deliveries.append(d)
         ep["deliveries"] = deliveries
         ep["muted_by"] = next((s["muted_by"] for s in steps if s["muted_by"]), None)