feat(telemetry): integrate OpenTelemetry observability stack with health metrics

- Add OpenTelemetry SDK, OTLP exporter, Prometheus integration
- Implement connection tracking with active/total/disconnection metrics
- Add health endpoint with uptime and connection counts
- Integrate tracing spans for socket events and engine messages
- Add metrics collection for event handling duration
- Update health endpoint to include live runtime state
- Add graceful telemetry shutdown in main function
- Implement engine session active metrics tracking
- Add namespace-specific attributes to connection metrics
- Introduce message edit history retrieval endpoint
- Add scheduled message CRUD operations and dispatcher
- Update Socket.IO event registration with observability
- Refactor component update to remove dead code allowance
- Add comprehensive environment variables documentation
- Implement detailed development guidelines in AGENTS.md

Cargo.toml

@@ -36,7 +36,14 @@ dashmap = "6"
 thiserror = "2"
 async-trait = "0.1"
 tracing = "0.1"
-tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+tracing-subscriber = { version = "0.3", features = ["env-filter", "json", "fmt", "registry"] }
+opentelemetry = { version = "0.32", features = ["trace", "metrics", "logs"] }
+opentelemetry_sdk = { version = "0.32", features = ["trace", "metrics", "logs", "rt-tokio"] }
+opentelemetry-otlp = { version = "0.32", features = ["trace", "metrics", "logs", "grpc-tonic", "http-proto", "tls-ring"] }
+tracing-opentelemetry = "0.33"
+opentelemetry-appender-tracing = "0.32"
+opentelemetry-prometheus = "0.32"
+prometheus = "0.14"
 fred = { version = "10", features = ["subscriber-client"] }
 async-nats = "0.38"
 futures-util = "0.3"