[router] Add OpenAI backend support - core function (#10254)

sgl-router/src/routers/mod.rs

@@ -17,6 +17,8 @@ pub mod header_utils;
 pub mod http;
 
 pub use factory::RouterFactory;
+// Re-export HTTP routers for convenience (keeps routers::openai_router path working)
+pub use http::{openai_router, pd_router, pd_types, router};
 
 /// Worker management trait for administrative operations
 ///