feat(demo): P3.5 inbox sidebar + inbox smoke (P3 complete)

message-demo gains a per-person Inbox rail (useInbox, done/snooze); sending
surfaces a NEEDS_REPLY item in the other pane; reading auto-resolves it.
smoke-inbox.mjs proves the event-driven flow end-to-end (send -> relay ->
projector -> inbox -> read -> DONE). Realtime smoke still passes.

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

apps/message-demo/package.json

@@ -10,6 +10,7 @@
   "dependencies": {
     "@insignia/iios-kernel-client": "workspace:*",
     "@insignia/iios-message-web": "workspace:*",
+    "@insignia/iios-inbox-web": "workspace:*",
     "react": "^19.0.0",
     "react-dom": "^19.0.0"
   },