feat(engagement): the email channel on the engine, and the Teams migration (engagement Phase 6)

Email becomes a DeliveryChannel driven by rules, and the Team pipeline stops being
its own thing. `teamNotify.forumPost` now emits an event; a rule decides who is
mailed, through which template, and how often at most. One walk goes forum write
-> events.emit -> rule -> outbox -> worker -> email channel -> template -> SMTP.

Seven decisions settled by the org lead before any code:

  - email only moves; the push tickle and the Discord bridge stay direct calls
  - the EVENT carries its access-checked audience, and `members` resolves to it
  - the four Team rules are seeded DISABLED, with an admin banner and a note
  - team_notification_prefs stays, read by the engine as a scoped preference
  - the payload wins and a structural projection fills the gaps
  - the digest keeps computing at send time; only its state generalizes
  - an unsubscribe token turns off the channel it names, and nothing else

Three defects found while building it:

  - `email.button` never absolutized its href, while image and itemList both
    did. Every rule-driven CTA would have been a dead relative link, because a
    trigger's url variables are validated site-relative by construction.
  - Phase 4a enqueued digest-mode recipients for a drain that Phase 6 decided
    not to build. An outbox row snapshots the payload and so has none of the
    three properties the digest design exists for, including the security one.
  - the digest's send-log row carried no address_hash while the instant row
    beside it did, which would have made half the mail uncorrelatable in Phase 9.

Also: engagement_digest_state + a replay-safe backfill, engagement_outbox.scope_key,
a v2 unsubscribe token that still verifies v1 forever, and the canonical
/public/engagement/unsubscribe pair with the old /public/teams path kept
permanently — mail is not editable once sent.

Verified with 1464 server tests, 324 client tests, and a live rig (MariaDB +
Mailpit + a real Team) covering the instant mail, the digest, the generic
template, a pre-migration unsubscribe link and the backfill's replay-safety.

Docs: RunicGateway/docs#TBD

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

client/src/routes/admin/views/EngagementRules.jsx

@@ -482,6 +482,30 @@ function RuleEditor({ catalog, segments, rule, onSaved, onCancel }) {
 
 // ── The screen ─────────────────────────────────────────────────────────────
 
+// ── The Phase 6 migration notice ───────────────────────────────────────────
+//
+// Team notifications used to be sent with no operator configuration at all;
+// ENGAGEMENT.md Phase 6 moved them onto rules, and the org lead's decision was to
+// seed those rules DISABLED rather than carve an exception into "nothing is on by
+// default". The consequence is a deployment whose Team email has stopped and
+// nobody has been told — which is G22's failure mode with a different cause — so
+// the screen that can fix it says so.
+//
+// It reads the RULES rather than a flag, so it disappears the moment one is
+// switched on and comes back if every one is switched off again. A deployment
+// that deleted them all sees nothing, which is right: they made that choice.
+const TEAM_TRIGGERS = [
+  'team.forum.post',
+  'team.announcement',
+  'team.member.joined',
+  'team.leadership.changed',
+]
+
+function teamRulesAllOff(rules) {
+  const team = rules.filter((r) => TEAM_TRIGGERS.includes(r.triggerId || r.trigger_id))
+  return team.length > 0 && team.every((r) => !r.enabled)
+}
+
 export default function EngagementRules() {
   const [catalog, setCatalog] = useState(null)
   const [segments, setSegments] = useState([])
@@ -558,6 +582,21 @@ export default function EngagementRules() {
 
   return (
     <section>
+      {teamRulesAllOff(rules) && (
+        <div
+          className="sans"
+          style={{
+            fontSize: '0.85rem', borderRadius: 8, padding: '10px 12px', marginBottom: 16,
+            border: '1px solid #7a6440', color: '#e0b070',
+          }}
+        >
+          <strong>Team notification emails are off.</strong> They used to be sent automatically; they
+          are now rules, and the four below arrived switched off so that nothing starts mailing on its
+          own. Switch on the ones this deployment wants — per-member preferences and per-Team mutes
+          still apply above them, and unsubscribe links in mail already sent still work.
+        </div>
+      )}
+
       <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', marginBottom: 16 }}>
         <p className="sans" style={{ margin: 0, fontSize: '0.86rem', color: 'var(--muted)', maxWidth: 640 }}>
           A rule turns an event into mail: which event, who hears about it, on which channels, and how