Update changelogs from fern repo (#5632)

Co-authored-by: dsinghvi <10870189+dsinghvi@users.noreply.github.com>

Author: fern-support

fern/products/cli-api-reference/cli-changelog/2026-05-27.mdx

@@ -1,3 +1,7 @@
+## 5.40.0
+**`(feat):`** Add hidden `fern docs theme delete --name <theme name>` CLI command to delete a named theme from an org. Includes a confirmation prompt (skippable with `--yes`).
+
+
 ## 5.39.0
 **`(feat):`** Add a `settings.search` object to `docs.yml` with two new options:
 - `prioritize-current-product`: boosts search results from the current