docs: update stability & changelog

docs/01-app/03-api-reference/04-functions/after.mdx

@@ -1,7 +1,7 @@
 ---
 title: after
 description: API Reference for the after function.
-version: unstable
+version: stable
 ---
 
 `after` allows you to schedule work to be executed after a response (or prerender) is finished. This is useful for tasks and other side effects that should not block the response, such as logging and analytics.
@@ -69,4 +69,5 @@ We recommend using `after` as it has been designed to consider other Next.js API
 
 | Version History | Description                  |
 | --------------- | ---------------------------- |
+| `v15.1.0`       | `after` is stable.           |
 | `v15.0.0-rc`    | `unstable_after` introduced. |