feat(KB-136): add shared badge pub/sub for multi-instance deployments

- Add BadgePubSub interface with Redis and in-memory adapters

- Implement cross-instance badge snapshot delivery via Redis pub/sub

- Add message validation, echo loop prevention, and structured caching

- Support graceful fallback to in-memory mode when Redis unavailable

- Update ServerOptions for dependency injection and add documentation

packages/dashboard/package.json

@@ -44,6 +44,7 @@
     "@xterm/addon-web-links": "^0.11.0",
     "@xterm/addon-webgl": "^0.18.0",
     "express": "^5.1.0",
+    "ioredis": "^5.6.0",
     "lucide-react": "^1.7.0",
     "multer": "^2.1.1",
     "node-pty": "^1.1.0-beta22",