feat(iios): @mentions via inbox fan-out + my-annotations query (pins/saves)

Mentions ride the existing event-driven inbox — no chat parsing in the kernel:
- send() carries an OPAQUE mentions[] (userIds) into the message event; the kernel
  never parses "@". The app supplies the notify-list.
- InboxProjector fans out a MENTION inbox item (new generic inbox kind) to each
  mentioned *participant* (never the sender), idempotent per source message; reading
  the thread resolves the reader's MENTION + NEEDS_REPLY items to DONE.
- New MENTION value in the generic IiosInboxItemKind taxonomy (migration).

Pins/saves reuse the annotation primitive; new generic query powers a Saved list:
- MessageService.listMyAnnotated(principal, type) + GET /v1/threads/my-annotations
  returns the caller's annotated messages (type "save") with thread context.

Tests: 182 pass (+4: mention fan-out, resolve-on-read, saved query, opaque mentions).
Verified live: mention→inbox delivery, read→resolve, pin/save persistence.

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

packages/iios-service/src/messaging/message.spec.ts

@@ -202,4 +202,28 @@ describe('Interaction annotations (generic reactions primitive)', () => {
     const msg = await s.send(threadId, alice, { content: 'secret' }, 'k1');
     await expect(s.toggleAnnotation(msg.id, bob, 'reaction', '👍')).rejects.toBeInstanceOf(PolicyDeniedError);
   });
+
+  it('listMyAnnotated returns the caller’s saved messages with thread context; others see none', async () => {
+    const s = gov();
+    const { threadId } = await s.openThread(null, alice, { membership: 'group', creatorRole: 'ADMIN', subject: 'Design' });
+    await s.addParticipant(threadId, alice, 'bob');
+    const msg = await s.send(threadId, alice, { content: 'save this' }, 'k1');
+    await s.toggleAnnotation(msg.id, alice, 'save', ''); // save is a personal annotation
+
+    const saved = await s.listMyAnnotated(alice, 'save');
+    expect(saved).toHaveLength(1);
+    expect(saved[0]).toMatchObject({ threadId, threadSubject: 'Design' });
+    expect(saved[0]?.message.content).toBe('save this');
+    expect(await s.listMyAnnotated(bob, 'save')).toHaveLength(0); // bob saved nothing
+  });
+
+  it('send carries an OPAQUE mentions[] into the message event (kernel never parses @)', async () => {
+    const s = svc();
+    const { threadId } = await s.openThread(null, alice);
+    await s.openThread(threadId, bob);
+    await s.send(threadId, alice, { content: 'hi @bob' }, 'k1', undefined, undefined, ['bob']);
+    const ev = await prisma.iiosOutboxEvent.findFirstOrThrow({ where: { eventType: 'com.insignia.iios.message.sent.v1' } });
+    const ce = ev.cloudEvent as { data: { mentions?: string[] } };
+    expect(ce.data.mentions).toEqual(['bob']);
+  });
 });