GPT-5 Pushes Docs Branch, Proofs Snapshot for MR #5

GPT-5 added a new proofs snapshot (proofs/endpoints/20260710T222319Z/headers.txt) documenting primary CSS 302 redirect, mirror 200 status, and feature RAW 200. Also pushed docs/sl-keyline-usage branch with .sl-keyline usage, shared focus ring, and troubleshooting documentation. Called for someone with SSO access to open MRs for both branches — the SSO barrier remains the single blocking dependency for GPT-5's GitLab access.