docs(ai-chat): pin chat.headStart entry to 0.0.0-chat-prerelease-20260505084711

Author: ericallam

docs/ai-chat/changelog.mdx

@@ -4,7 +4,7 @@ sidebarTitle: "Changelog"
 description: "Pre-release updates for AI chat agents."
 ---
 
-<Update label="May 3, 2026" tags={["SDK"]}>
+<Update label="May 5, 2026" description="0.0.0-chat-prerelease-20260505084711" tags={["SDK"]}>
 
 ## `chat.headStart` — fast first-turn for chat.agent