feat(email): the report, invites, resets and test sends go through the outbox; only it talks SMTP (#5508)

#5508 "Every other email through the outbox: weekly report, invites,
password resets, and the test buttons" (milestone 501).

- outbox.send_each queues one email per reader (claimed, so the sender
  doesn't take it too) and tries them at once, for a page that answers
  with what happened; outbox.said words the result. attempt takes a cfg
  for a test of the form's unsaved settings and returns the settled rows.
- Weekly report (scheduled and Send now) and invites: queued, tried at
  once; one the server couldn't take yet is retried for an hour. An invite
  that didn't go shows its link with the reason, as before.
- Password reset: queued in the reset link's own transaction; the sender
  delivers it on its next tick.
- Settings -> Notifications test email and a rule's Send test: queued and
  recorded with retry=False, tried once (System 156 ruling).
- Removed mail.send, notifications._send_email and _smtp_send_sync;
  dispatch_notifications is webhook only. A guard asserts only the outbox
  (and smtp_open itself) opens an SMTP connection, with a self-test.

Also fixes run 8941 (#5507's integration test): its Also-send-to
addresses were "@test", which is_real_address rightly drops; they are
example.com now.

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

tests/integration/test_alert_email_outbox.py

@@ -81,7 +81,7 @@ def test_alerts_in_one_window_are_one_email_and_each_event_records_it(app, monke
     from steward.core import outbox
 
     tag = uuid.uuid4().hex[:8]
-    extra = f"oncall-{tag}@test"
+    extra = f"oncall-{tag}@example.com"
     app.config["SMTP"] = {"host": "mx.test", "port": 587, "from": "steward@test",
                           "recipients": [extra], "tz": "America/New_York"}
     t0 = datetime(2026, 10, 9, 12, 0, tzinfo=timezone.utc)
@@ -142,7 +142,7 @@ def test_an_email_whose_alerts_were_deleted_fails_and_says_so(app, monkeypatch):
     from steward.models.alerts import AlertEvent
 
     tag = uuid.uuid4().hex[:8]
-    extra = f"gone-{tag}@test"
+    extra = f"gone-{tag}@example.com"
     app.config["SMTP"] = {"host": "mx.test", "port": 587, "from": "steward@test", "recipients": [extra]}
     monkeypatch.setattr(outbox, "deliver_sync", lambda cfg, msgs: [None] * len(msgs))
     t0 = datetime.now(timezone.utc)
@@ -155,8 +155,8 @@ def test_an_email_whose_alerts_were_deleted_fails_and_says_so(app, monkeypatch):
         async with app.db_sessionmaker() as s:
             async with s.begin():
                 await s.execute(delete(AlertEvent).where(AlertEvent.id == ev))
-        states = await outbox.attempt(app, [row.id])
-        return states[row.id], row.id
+        done = await outbox.attempt(app, [row.id])
+        return done[row.id].state, row.id
 
     state, rid = asyncio.run(_go())
     assert state == "failed"