push architecture slice 1: core event bus + /api/events SSE channel (notify->fetch infra, no consumers yet)

src/server/index.ts

@@ -5,6 +5,7 @@
  */
 
 export * from "./chat-handler.ts";
+export * from "./events-stream.ts";
 export * from "./chats.ts";
 export * from "./practice.ts";
 export * from "./graph.ts";