feat(engagement): the in-app channel, core and web (engagement Phase 7)

ENGAGEMENT.md Phase 7. `user_notifications`, the in-app DeliveryChannel, the
four inbox routes, and the web surface — plus the two pieces earlier phases
assigned here that Phase 7's own acceptance line omits.

Four decisions settled by the org lead before any code:

1. `inapp` defaults to `instant` — the only channel that does. Push wakes a
   device somebody is holding and email leaves the building, so both are asked
   for; an inbox item is a row on a page the user chose to open. Left `off` the
   channel ships dead.
2. The phase takes push's `deliver` (§2603) and the web per-channel preferences
   screen (Phase 3's as-built), neither of which its own bullets mention.
3. The inbox takes `/auth/me/notifications` and `/account/notifications`; the
   preferences screen moves to `…/settings`. The plain word belongs to the
   content, which is what the bell opens.
4. `ctx.inbox.push` honours the user's in-app preference when `triggerId` names
   a registered trigger, and writes when it does not.

Server
- `user_notifications` + `model/userNotifications/`. The dedupe UNIQUE is scoped
  to the USER, narrower than the outbox's `(rule, user, channel)`: an inbox has
  no channel dimension, so two rows for one event would be one item shown twice.
- `engagement/inappChannel.js` — renders by block ROLE (first heading → title,
  first button → url, the rest → body) and inserts. `pushChannel.js` — a
  content-free `{stream, ref}` tickle whose ref deep-links the inbox row.
- `engine.liveChannels` orders `inapp` first (`CHANNEL_ORDER`) so that ref
  resolves on the first sweep. An ordering, not a dependency.
- `templates.renderInappByKey` + `resolveTemplate` extracted from `renderByKey`,
  so both channels take the same fallback chain.
- `inapp.event` seed → seedVersion 2: it named `body`/`url`, which nothing
  supplies. Renamed to the structural vocabulary the projection fills in.
- `utils/userNotificationsPrune.js` — nightly, READ items only, horizon in
  `settings.user_notifications_retain_days` (default 90).
- `GET /auth/me/notifications`, `…/unread-count`, `POST …/:id/read`,
  `POST …/read-all`. Swagger + route manifest + four component schemas.

Web
- `NotificationBell` in all three headers, polling its badge once a minute and
  pausing while the tab is hidden. `PlayerInbox` at `/account/notifications`.
- The preferences screen becomes a channel matrix over
  `/auth/me/notifications/channels` — a strict superset of the push-only stream
  list it replaces. The two legacy endpoints are untouched, so the shipped
  Android app keeps its wire shape.
- Staff get the same two screens at `/admin/notifications…`: `RequirePlayer`
  keeps them out of `/account`, so without this the inbox was unreachable for
  every non-player account. `lib/notificationPaths.js` is the one mapping.

Verified: 28 new server tests (5 of them against a real MariaDB, for the three
index/statement properties that are a server contract rather than a reading of
this code) + 3 client. Server suite green, client 327 green. A live rig walked
the whole path: two rules on one event produced three outbox rows and exactly
one inbox item, the tickle carried `ref: notification:2`, and the retention
sweep dropped an aged read row while keeping an equally aged unread one.

Docs: RunicGateway/docs#TBD, RunicGateway/runicgateway.com#TBD

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

server/src/engagement/coreChannels.js

@@ -17,6 +17,8 @@
 
 const { registerDeliveryChannel } = require('./channels')
 const emailChannel = require('./emailChannel')
+const pushChannel = require('./pushChannel')
+const inappChannel = require('./inappChannel')
 
 const CHANNELS = [
   {
@@ -44,6 +46,10 @@ const CHANNELS = [
     // there is nothing to roll up. Ten events are ten wakeups or one; either way
     // the app pulls the same inbox.
     supportsDigest: false,
+    // Phase 7: the oldest sink is the last to get a `deliver`, because until the
+    // inbox existed there was nothing for a content-free tickle to point at.
+    addressFor: pushChannel.addressFor,
+    deliver: pushChannel.deliver,
   },
   {
     id: 'email',
@@ -66,13 +72,25 @@ const CHANNELS = [
     label: 'On the site',
     description: 'An item in your notification inbox on the website and in the app.',
     carriesContent: true,
-    // Opt-IN like the other two, and for a reason particular to this channel: the
-    // inbox does not exist until Phase 7. A default of 'instant' would mean every
-    // user is opted into a surface that has no rows and no screen, and the first
-    // thing Phase 7 shipped would be a backlog. Whether the inbox is opt-out once
-    // it is real is a Phase 7 decision with a live surface to look at.
-    defaultMode: 'off',
+    // **Opt-OUT, and the only one of the three that is** — settled by the org
+    // lead 2026-08-31, which is the Phase 7 decision this comment used to defer.
+    //
+    // The argument against a live default was never about in-app: it was that
+    // push wakes a device the user is holding and email leaves the building, so
+    // both must be asked for. An inbox item does neither. It is a row on a page
+    // the user chose to open, on this deployment, costing them one glance — and
+    // left at 'off' the surface would ship dead, because no rule could reach
+    // anyone until every user found a toggle for a channel they had never seen
+    // deliver anything. The backlog Phase 3 worried about cannot happen either:
+    // the table is empty at cutover, rules default to `enabled = 0`, and every
+    // rule carries a per-hour ceiling.
+    defaultMode: 'instant',
+    // Instant-only, and unlike push the reason is not that batching is
+    // meaningless — it is that the inbox IS the batch. A digest of inbox items
+    // is a list of things already sitting in a list.
     supportsDigest: false,
+    addressFor: inappChannel.addressFor,
+    deliver: inappChannel.deliver,
   },
 ]