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/src/threads/threads.controller.ts

@@ -54,6 +54,19 @@ export class ThreadsController {
     return this.threads.getMessages(id);
   }
 
+  /** Mute / unmute notifications from this thread for the caller. */
+  @Post(':id/mute')
+  @HttpCode(200)
+  async mute(@Param('id') id: string, @Headers('authorization') auth?: string) {
+    return this.messages.muteThread(id, this.principal(auth), true);
+  }
+
+  @Post(':id/unmute')
+  @HttpCode(200)
+  async unmute(@Param('id') id: string, @Headers('authorization') auth?: string) {
+    return this.messages.muteThread(id, this.principal(auth), false);
+  }
+
   /** REST/polling fallback for native send (same write as the socket path). */
   @Post(':id/messages')
   @HttpCode(201)