Add comprehensive documentation for Linear Void project

- Created README.md in docs folder outlining project structure and documentation links.
- Added SECURITY.md detailing the security model, threat model, authentication, transport security, network isolation, and incident response procedures.
- Introduced SETUP.md providing a detailed setup guide for local and production environments, including prerequisites, environment setup, and Gitea integration.
- Added STREAMING.md outlining the streaming pipeline, including production flow, source-media contract, playout and HLS packaging, cache contract, player behavior, and monitoring.
- Updated architecture documentation to include links to new SETUP.md and STREAMING.md files for better navigation.

docs/architecture/README.md

@@ -87,10 +87,12 @@
 
 ## Companion Documentation
 
-- [API.md](../../API.md) - Implemented WebSocket and REST API reference.
-- [DEPLOYMENT.md](../../DEPLOYMENT.md) - Production deployment and operational runbook.
-- [MONITORING.md](../../MONITORING.md) - Metrics, dashboards, and monitoring troubleshooting.
-- [SECURITY.md](../../SECURITY.md) - Security model, controls, and hardening baseline.
+- [API.md](../API.md) - Implemented WebSocket and REST API reference.
+- [DEPLOYMENT.md](../DEPLOYMENT.md) - Production deployment and operational runbook.
+- [MONITORING.md](../MONITORING.md) - Metrics, dashboards, and monitoring troubleshooting.
+- [SECURITY.md](../SECURITY.md) - Security model, controls, and hardening baseline.
+- [SETUP.md](../SETUP.md) - Test lab setup, local development, and CI/CD workflow.
+- [STREAMING.md](../STREAMING.md) - Streaming architecture, playout, and delivery details.
 
 ## Introduction and Goals