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/templates/alerts/_history_page.html

@@ -48,11 +48,20 @@
           <span class="badge badge-yellow" title="A maintenance window muted this notification">muted · {{ ep.muted_by }}</span>
           {% if ep.released %}<div class="cell-note">notified when the window ended</div>{% endif %}
           {% endif %}
-          {% for label, sent, error in ep.deliveries %}
+          {# Each channel's outcome; an email through the outbox (#5509) also
+             says when it sends, or how its retries stand, or why it failed. #}
+          {% for d in ep.deliveries %}
           <div>
-            {% if sent %}<span class="badge badge-green">{{ label }} sent</span>
-            {% else %}<span class="badge badge-red">{{ label }} failed</span>
-            {% if error %}<div class="cell-note" style="max-width:28rem;overflow-wrap:anywhere;">{{ error }}</div>{% endif %}
+            {% if d.state == "sent" %}<span class="badge badge-green">{{ d.label }} sent</span>
+            {%- if d.at %} <span class="tone-dim">{{ d.at|when }}</span>{% endif %}
+            {% elif d.state == "held" %}<span class="badge badge-yellow">{{ d.label }} gathering</span>
+            <div class="cell-note">waiting for other alerts; sends {{ d.at|when }}</div>
+            {% elif d.state == "sending" %}<span class="badge badge-yellow">{{ d.label }} sending</span>
+            {% elif d.state == "retrying" %}<span class="badge badge-yellow">{{ d.label }} retrying</span>
+            <div class="cell-note" style="max-width:28rem;overflow-wrap:anywhere;">attempt {{ d.attempts }}
+              {%- if d.at %}, next {{ d.at|when }}{% endif %}{% if d.error %}: {{ d.error }}{% endif %}</div>
+            {% else %}<span class="badge badge-red">{{ d.label }} failed</span>
+            {% if d.error %}<div class="cell-note" style="max-width:28rem;overflow-wrap:anywhere;">{{ d.error }}</div>{% endif %}
             {% endif %}
           </div>
           {% endfor %}