feat(threads): governed group settings — rename, list members, remove participant

- MessageService.renameThread / removeParticipant / listParticipants,
  each fail-closed via OPA (kernel stays generic — no dm/group branching)
- dev OPA: iios.thread.update + iios.thread.participant.remove rules
  (group requires ADMIN; ungoverned threads unchanged)
- REST: PATCH /v1/threads/:id, GET + DELETE /v1/threads/:id/participants
- tests: admin renames/removes, member is denied, member list carries roles
  (message.spec + dev-opa.port.spec)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/iios-service/src/platform/dev-opa.port.spec.ts

@@ -33,6 +33,22 @@ describe('DevOpaPort (dev policy plane — membership rules)', () => {
     expect(asAdmin.allow).toBe(true);
   });
 
+  it('group rename (thread.update) requires ADMIN; ungoverned threads allow it', async () => {
+    const asMember = await opa.decide({ action: 'iios.thread.update', membership: 'group', callerRole: 'MEMBER' });
+    expect(asMember.allow).toBe(false);
+    expect(asMember.obligations[0]?.reason).toMatch(/admin/);
+    expect((await opa.decide({ action: 'iios.thread.update', membership: 'group', callerRole: 'ADMIN' })).allow).toBe(true);
+    expect((await opa.decide({ action: 'iios.thread.update' })).allow).toBe(true); // no membership attr → allow
+  });
+
+  it('group remove requires ADMIN; a member on an ungoverned thread may remove', async () => {
+    const asMember = await opa.decide({ action: 'iios.thread.participant.remove', membership: 'group', callerRole: 'MEMBER' });
+    expect(asMember.allow).toBe(false);
+    expect(asMember.obligations[0]?.reason).toMatch(/admin/);
+    expect((await opa.decide({ action: 'iios.thread.participant.remove', membership: 'group', callerRole: 'ADMIN' })).allow).toBe(true);
+    expect((await opa.decide({ action: 'iios.thread.participant.remove', callerRole: 'MEMBER' })).allow).toBe(true);
+  });
+
   it('self-join is governed only on membership threads', async () => {
     // generic / support thread (no membership attr) → open join, unchanged
     expect((await opa.decide({ action: 'iios.thread.join', alreadyMember: false })).allow).toBe(true);