feat: live messages via SSE + real client IP

- backend: SSE endpoint /api/messages/stream backed by Redis pub/sub
- backend: read real client IP via getConnInfo (fallback for x-forwarded-for)
- backend: CORS allow any origin (dev: LAN access from phone)
- frontend: useMessages subscribes via EventSource, auto-reconnect, merges new messages/replies live
- frontend: vite host:true to expose dev server on LAN

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/vite.config.ts

@@ -11,5 +11,6 @@ export default defineConfig({
   },
   server: {
     port: 5173,
+    host: true,
   },
 });