feat(iios): notification engine — presence-gated Web Push (engine phase)

Generic notification engine: reacts to message.sent and runs three gates before
delivering — policy (DM always; group only on @mention or reply-to-you), presence
(skip if the recipient is focused on that thread), mute (per-thread). Delivery via a
swappable NotificationPort (Web Push/VAPID adapter); a 'gone' (404/410) prunes the sub.

- PresenceService + gateway `focus_thread` signal + disconnect cleanup (room membership
  != viewing, since the sidebar joins every thread room).
- IiosNotificationSubscription table + `muted` on IiosThreadParticipant (migration).
- Endpoints: GET vapid-public-key, POST/DELETE subscribe, POST threads/:id/mute|unmute;
  listThreads returns the caller's `muted`.
- DM-vs-group read from the opaque `membership` attribute in the notification POLICY only
  — kernel stays generic (grep-verified).

Tests: 13 new (3 gates + reply-to-you + prune + web-push adapter states); full suite 205
green. Verified live: module boots, subscribe stored, mute/unmute round-trips.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/prisma/migrations/20260709133349_add_notifications/migration.sql

@@ -0,0 +1,30 @@
+-- AlterTable
+ALTER TABLE "IiosThreadParticipant" ADD COLUMN     "muted" BOOLEAN NOT NULL DEFAULT false;
+
+-- CreateTable
+CREATE TABLE "IiosNotificationSubscription" (
+    "id" TEXT NOT NULL,
+    "scopeId" TEXT NOT NULL,
+    "actorId" TEXT NOT NULL,
+    "kind" TEXT NOT NULL DEFAULT 'webpush',
+    "endpoint" TEXT NOT NULL,
+    "p256dh" TEXT NOT NULL,
+    "auth" TEXT NOT NULL,
+    "userAgent" TEXT,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "lastSeenAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "IiosNotificationSubscription_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "IiosNotificationSubscription_endpoint_key" ON "IiosNotificationSubscription"("endpoint");
+
+-- CreateIndex
+CREATE INDEX "IiosNotificationSubscription_actorId_idx" ON "IiosNotificationSubscription"("actorId");
+
+-- AddForeignKey
+ALTER TABLE "IiosNotificationSubscription" ADD CONSTRAINT "IiosNotificationSubscription_scopeId_fkey" FOREIGN KEY ("scopeId") REFERENCES "IiosScope"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "IiosNotificationSubscription" ADD CONSTRAINT "IiosNotificationSubscription_actorId_fkey" FOREIGN KEY ("actorId") REFERENCES "IiosActorRef"("id") ON DELETE RESTRICT ON UPDATE CASCADE;

packages/iios-service/prisma/schema.prisma

@@ -309,6 +309,7 @@ model IiosScope {
   supportQueues IiosSupportQueue[]
   tickets       IiosTicket[]
   callbacks     IiosCallbackRequest[]
+  notificationSubscriptions IiosNotificationSubscription[]
 
   @@index([orgId, appId, tenantId])
 }
@@ -358,6 +359,7 @@ model IiosActorRef {
   ticketsRequested   IiosTicket[]            @relation("TicketRequester")
   ticketsAssigned    IiosTicket[]            @relation("TicketAssignee")
   callbacksRequested IiosCallbackRequest[]
+  notificationSubscriptions IiosNotificationSubscription[]
 }
 
 /// A configured channel surface (PORTAL in P1).
@@ -412,12 +414,32 @@ model IiosThreadParticipant {
   actorId         String
   actor           IiosActorRef @relation(fields: [actorId], references: [id])
   participantRole String       @default("MEMBER")
+  muted           Boolean      @default(false)
   joinedAt        DateTime     @default(now())
   leftAt          DateTime?
 
   @@id([threadId, actorId])
 }
 
+/// A device/browser push subscription for an actor (Web Push endpoint + keys).
+/// The notification engine delivers to these when the actor is absent.
+model IiosNotificationSubscription {
+  id         String       @id @default(cuid())
+  scopeId    String
+  scope      IiosScope    @relation(fields: [scopeId], references: [id], onDelete: Cascade)
+  actorId    String
+  actor      IiosActorRef @relation(fields: [actorId], references: [id])
+  kind       String       @default("webpush")
+  endpoint   String       @unique
+  p256dh     String
+  auth       String
+  userAgent  String?
+  createdAt  DateTime     @default(now())
+  lastSeenAt DateTime     @default(now())
+
+  @@index([actorId])
+}
+
 /// The semantic envelope. Idempotent per (scope, idempotencyKey).
 model IiosInteraction {
   id                  String              @id @default(cuid())