docs: Add Sentry deployment documentation

- Create docs/sentry.md: Complete Sentry self-hosted deployment guide
  * Architecture overview with distributed system components
  * Core services: Relay, Kafka, Snuba, ClickHouse, PostgreSQL, Redis, SeaweedFS
  * Data flow and storage requirements
  * Management via slcompose orchestrator
  * Backup requirements documentation

- Update AI_CONTEXT.md: Add Sentry to core services
  * List Sentry as error tracking & observability platform
  * Add sentry.silveressence.net domain mapping

- Update README.md: Add Sentry to running services
  * Include in comprehensive services list

- Update roadmap.md: Mark Sentry as completed
  * Move from planned to completed section
  * Document all deployed components
  * List completed validation items
  * Reference deployment documentation

- Update services.md: Full Sentry service documentation
  * Add running Sentry service section
  * Document architecture, networking, and management
  * Remove from Phase 2 planned deployments
  * Link to detailed deployment guide

docs/AI_CONTEXT.md

@@ -29,6 +29,7 @@ Public IP: 51.255.83.140
 * Gitea Actions Runner (`silverlinux-runner`)
 * DbGate
 * Xray
+* Sentry (Error Tracking & Observability)
 * Prometheus
 * Grafana
 * Node Exporter
@@ -49,6 +50,8 @@ nuget.silveressence.net -> BaGet (through Nginx Proxy Manager)
 
 dbgate.silveressence.net -> DbGate (through Nginx Proxy Manager)
 
+sentry.silveressence.net -> Sentry (through Nginx Proxy Manager)
+
 Xray -> Public tunneling endpoint through proxy network
 
 ## Secrets