update changelogs

Author: thesandlord

fern/products/cli-api-reference/cli-changelog/2026-09-11.mdx

@@ -1,3 +1,9 @@
+## 5.121.0
+**`(feat):`** Add an optional `disclaimer` field to the `ai-search`/`ai-chat` docs.yml config.
+It overrides the disclaimer shown in the Ask Fern chat (default:
+"Responses are generated using AI and may contain mistakes.").
+
+
 ## 5.120.5
 **`(fix):`** Fix `theme.tabs.placement` / `theme.tabs.alignment` being sent to the docs publishing API in lowercase,
 which caused `fern generate --docs` to fail with `config.theme.tabs: Invalid input` even though