docs(admin): Team notification emails are engagement rules now

The Teams page gains the section engagement Phase 6 owes it. The operator-facing
fact is the one that has to land first: Team emails used to send with no
configuration and now arrive switched off, so nobody gets them until a rule is
turned on in Admin → Engagement → Rules.

Also says what each of the four seeded rules sends and why the two roster ones
ship off, that a rule decides whether the site sends at all while members still
choose per Team, why a digest is re-read at send time, and that unsubscribe links
in mail already sent still work — now stopping the emails they came with without
also silencing that Team's push.

Site: RunicGateway/website#TBD · Docs: RunicGateway/docs#TBD

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

src/content/docs/docs/administration/teams.mdx

@@ -48,6 +48,51 @@ Two rules are structural rather than settings:
   about a leader has to reach someone above them. See
   [Moderation](/docs/administration/moderation/).
 
+## Team notification emails
+
+**Team emails are sent by the engagement rules, and they arrive switched off.**
+
+Someone posting in a Team forum used to send mail with no configuration at all. It now goes
+through the same engine as everything else the site sends: the forum post raises an event,
+an **engagement rule** decides who is told and through which message template, and the
+outbox delivers it. Push notifications to the app and the Discord bridge below are
+unaffected — only the email moved.
+
+The practical consequence on an existing site: **nobody gets Team email until you turn a
+rule on.** Open **Admin → Engagement → Rules**. Four rules are waiting there, one per Team
+event, all switched off, and the screen says so at the top for as long as they all are.
+Switch on the ones your site wants.
+
+| Rule | Sends when |
+|---|---|
+| **Team forum posts** | someone posts a new thread or reply |
+| **Team announcements** | a leader posts an announcement |
+| **Team — new member** | someone joins, at most once an hour per person |
+| **Team — leadership change** | a new leader is named, at most once an hour per person |
+
+The first two are the ones most sites want. The last two describe things that already show
+up on the Team's activity feed and arrive from a sweep rather than from a person doing
+something — which is why they ship off and with a cooldown.
+
+<Aside type="note" title="Members still control their own mail">
+A rule decides whether the site sends at all. Each member still chooses, per Team, between
+no email, one message per post, and a daily digest — on their own notifications screen or
+through the unsubscribe link in any Team email. Turning a rule on does not sign anybody up.
+</Aside>
+
+**Digests are re-read at the moment they are sent**, not assembled as posts arrive. A site
+that was down for two days sends one digest rather than two days of backlog, a post a
+moderator hid is not in it, and somebody who lost access to a forum between the post and the
+send does not receive it.
+
+**Unsubscribe links keep working.** A link in mail sent before this change still does what
+it says. What changed is that it is now precise: it stops the emails it came with and leaves
+that Team's push notifications alone, where before it silenced both.
+
+You can change what any of these messages say — see
+[Message templates](/docs/administration/message-templates/) — and see who was actually
+sent what in **Admin → Engagement → Send log**.
+
 ## The Discord bridges
 
 Two integrations, both optional, both configured from **Admin → Teams**.