feat(messenger): CRM consumes @insignia/iios-messaging-ui instead of embedding

The messenger tab now renders the shared SDK's <Messenger>, not the bespoke
in-CRM implementation. The CRM only supplies transport + theme:

- CrmMessagingAdapter implements the SDK's MessagingAdapter over the be-crm
  data door (crm.messenger.conversation.list/open, history, send, directory);
  live updates via a 4s poll for now (socket realtime is a follow-up that
  reuses messenger-socket.tsx). Tenancy/auth stay server-side.
- messenger-sdk.tsx wires MessagingProvider + adapter (live = CrmMessagingAdapter,
  demo = the SDK MockAdapter), themed by mapping --miu-* tokens to the CRM
  design system.
- dashboard renders <MessengerSdk/>; the old messenger.tsx is left in place
  for rollback and will be deleted once this is proven live.

NOTE: the SDK is installed from a local tarball (file:) for verification since
it isn't published yet. For deploy: publish @insignia/iios-messaging-ui to the
registry and change the dep to a version range. transpilePackages covers ESM.

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

package.json

@@ -11,6 +11,7 @@
   "dependencies": {
     "@abe-kap/appshell-sdk": "^0.2.6",
     "@insignia/iios-kernel-client": "^0.1.4",
+    "@insignia/iios-messaging-ui": "file:../iios/packages/iios-messaging-ui/insignia-iios-messaging-ui-0.1.0.tgz",
     "clsx": "^2.1.1",
     "lucide-react": "^1.21.0",
     "next": "16.2.9",