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

telemetry/config.rs

@@ -0,0 +1,85 @@
+/// Telemetry configuration, populated from environment variables.
+///
+/// Follows the OpenTelemetry environment variable specification:
+/// <https://opentelemetry.io/docs/specs/otel/configuration/sdk-environment-variables/>
+#[derive(Debug, Clone)]
+pub struct TelemetryConfig {
+    pub service_name: String,
+    pub service_version: String,
+    pub otlp_endpoint: String,
+    pub otlp_protocol: OtlpProtocol,
+    pub traces_enabled: bool,
+    pub metrics_enabled: bool,
+    pub logs_enabled: bool,
+    pub log_format: LogFormat,
+    pub log_level: String,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum OtlpProtocol {
+    Grpc,
+    HttpProtobuf,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum LogFormat {
+    Json,
+    Pretty,
+}
+
+impl Default for TelemetryConfig {
+    fn default() -> Self {
+        Self {
+            service_name: env_or("OTEL_SERVICE_NAME", "imks"),
+            service_version: env_or("OTEL_SERVICE_VERSION", env!("CARGO_PKG_VERSION")),
+            otlp_endpoint: env_or(
+                "OTEL_EXPORTER_OTLP_ENDPOINT",
+                "http://localhost:4317",
+            ),
+            otlp_protocol: detect_otlp_protocol(),
+            traces_enabled: env_bool("OTEL_TRACES_ENABLED", true),
+            metrics_enabled: env_bool("OTEL_METRICS_ENABLED", true),
+            logs_enabled: env_bool("OTEL_LOGS_ENABLED", true),
+            log_format: detect_log_format(),
+            log_level: env_or("RUST_LOG", "info"),
+        }
+    }
+}
+
+impl TelemetryConfig {
+    pub fn from_env() -> Self {
+        Self::default()
+    }
+}
+
+fn env_or(key: &str, default: &str) -> String {
+    std::env::var(key).unwrap_or_else(|_| default.to_string())
+}
+
+fn env_bool(key: &str, default: bool) -> bool {
+    std::env::var(key)
+        .map(|v| matches!(v.to_lowercase().as_str(), "true" | "1" | "yes" | "on"))
+        .unwrap_or(default)
+}
+
+fn detect_otlp_protocol() -> OtlpProtocol {
+    match std::env::var("OTEL_EXPORTER_OTLP_PROTOCOL")
+        .unwrap_or_default()
+        .to_lowercase()
+        .as_str()
+    {
+        "http/protobuf" | "http/binary" => OtlpProtocol::HttpProtobuf,
+        _ => OtlpProtocol::Grpc, // default to gRPC as project already depends on tonic
+    }
+}
+
+fn detect_log_format() -> LogFormat {
+    match std::env::var("LOG_FORMAT")
+        .unwrap_or_else(|_| "json".to_string())
+        .to_lowercase()
+        .as_str()
+    {
+        "pretty" | "text" | "console" => LogFormat::Pretty,
+        _ => LogFormat::Json, // default to JSON for structured logging
+    }
+}