feat: add service graph as enterprise-only feature

Service graph automatically discovers service topology from distributed traces.

OSS includes:
- API routing endpoints (gated with enterprise feature flag)
- UI components (functional only with enterprise backend)
- Configuration options

Enterprise includes:
- 256-shard concurrent edge store with LRU eviction
- Span matching and processing logic
- Prometheus metrics and background workers

src/handler/http/request/traces/mod.rs

@@ -26,6 +26,9 @@ use hashbrown::HashMap;
 use serde::Serialize;
 use tracing::{Instrument, Span};
 
+// Re-export service graph API handlers
+#[cfg(feature = "enterprise")]
+pub use crate::service::traces::service_graph::{get_service_graph_metrics, get_store_stats};
 use crate::{
     common::{
         meta::{self, http::HttpResponse as MetaHttpResponse},

src/handler/http/router/mod.rs

@@ -612,7 +612,9 @@ pub fn get_service_routes(svc: &mut web::ServiceConfig) {
         .service(re_pattern::delete)
         .service(re_pattern::test)
         .service(domain_management::get_domain_management_config)
-        .service(domain_management::set_domain_management_config);
+        .service(domain_management::set_domain_management_config)
+        .service(traces::get_service_graph_metrics)
+        .service(traces::get_store_stats);
 
     #[cfg(feature = "cloud")]
     let service = service