clarify auth requirement for cli

Author: skarim

docs/src/content/docs/getting-started/quick-start.md

@@ -19,6 +19,10 @@ Stacked PRs is currently in private preview. This feature will **not work** unle
 gh extension install github/gh-stack
 ```
 
+:::note[Authentication]
+The `gh stack` CLI requires OAuth authentication via `gh auth login`. Personal access tokens (PATs) are not supported.
+:::
+
 ## Set Up AI Agent Integration
 
 If you use AI coding agents (like GitHub Copilot), install the gh-stack skill so they know how to work with Stacked PRs:

docs/src/content/docs/reference/cli.md

@@ -11,6 +11,10 @@ gh extension install github/gh-stack
 
 Requires the [GitHub CLI](https://cli.github.com/) (`gh`) v2.0+.
 
+:::note[Authentication]
+The `gh stack` CLI requires OAuth authentication via `gh auth login`. Personal access tokens (PATs) are not supported.
+:::
+
 ---
 
 ## Stack Management