Update changelogs from fern repo (#498)

Co-authored-by: aditya-arolkar-swe <[email protected]>

Author: fern-support

fern/products/cli-api-reference/cli-changelog/2025-08-18.mdx

@@ -1,3 +1,6 @@
+## 0.66.19
+**`(chore):`** Handle multipart/mixed content types in endpoint responses.
+
 ## 0.66.18
 **`(chore):`** Updated allOf scheme parsing to grab additionalProperties flag