feat(31-02): export chat types from central index

- Add chat.ts to type re-export hub
- Follows existing pattern (quickstart, nodes, etc.)

src/types/index.ts

@@ -13,3 +13,4 @@ export * from "./models";
 export * from "./workflow";
 export * from "./api";
 export * from "./quickstart";
+export * from "./chat";