~x-ai/grok-latest → A (4:1)

Commit A adds lasting product infrastructure: browser session cookies, web login/logout, POST /post ingest, and full public/private room forum routing and pages (ThreadNav, ACL-gated room views, compose forms). Commit B improves one existing surface—vote-compare fullscreen chrome, edge-history sort/ratio alignment, and preview morph—plus CSS/tests, which is real but narrower UX polish rather than core wiring.