[codex] clean up OAuth 2.0 docs styling, anchors, and OIDC quickstart guidance (#104)

* [codex] remove emoji styling from oauth guide

* [codex] remove final oauth guide emoji markers

* [codex] fix oauth guide faq anchor links

* [codex] add stable oauth guide user-link anchor

* [codex] move oauth guide user-link section out of collapsed details

* [codex] collapse oauth guide user-link code examples

Author: basit3407