refactor: modularize chat backend, update docs for .m4s segments

README.md

@@ -15,7 +15,7 @@
 The architecture (detailed in [`docs/architecture/README.md`](docs/architecture/README.md)) uses:
 
 - Hetzner Ashburn VPS for playout (FFmpeg + MediaMTX/SRS) and chat _(planned production; currently test lab at 192.168.88.40)_.
-- Cloudflare R2 + CDN with aggressive immutable caching of HLS `.ts` segments ($0 egress).
+- Cloudflare R2 + CDN with aggressive immutable caching of `.m4s` segments ($0 egress).
 - Lightweight static frontend and WebSocket chat backend.
 - Gitea self-hosted CI/CD (Actions) and Container Registry.
 
@@ -211,6 +211,7 @@ Contributions, issues, and further evolution (LL-HLS, ABR, multi-channel, E2EE)
 - [DEPLOYMENT.md](DEPLOYMENT.md) - Production deployment and operations guide.
 - [MONITORING.md](MONITORING.md) - Prometheus and Grafana setup and troubleshooting.
 - [SECURITY.md](SECURITY.md) - Security controls, hardening checklist, and incident baseline.
+- [Scaling Playbook](docs/operations/scaling-performance-playbook.md) - Performance test method, thresholds, and scaling decision flow.
 - [Architecture Documentation](docs/architecture/README.md) - Full arc42 template with diagrams and decisions.
 - [ADRs](docs/architecture/adr/) - Detailed decision records (ADR-001 to ADR-007).