Add Enable SSO page to docs Getting Started

Jessica asked in #website thread 1780627524.654729 to add an 'Enable SSO' page under the Getting Started section of docs.texturehq.com, placed right after 'Signing Up'. Source content lives in the Notion page she shared (https://www.notion.so/texturehq/Single-Sign-On-SSO-3745b7fc9f3d80d98aa3e8ac0294b67d). Notion is a JS-rendered SPA behind a login wall — Web-Dave cannot programmatically read content or images. Replied in thread asking Jessica to paste the copy + drop image attachments in Slack. Once content lands: create apps/docs/content/getting-started/enable-sso.md with sidebar_position 3 (bumping quickstart.mdx to 4), save attached images into apps/docs/static/img/getting-started/ or similar, open PR, share preview, get Jessica approval, merge. Jessica is OOO June 5-12, so this may sit until she returns.