Value-prop side panel added (UX audit #12 fix). v15 had a single 400px column with no pitch — the audit flagged "Sign in with email and password" as the full pitch.
Continue with Google added as the primary path. Email as fallback. Per UX audit.
Studio variant: when ?next=/studio is set, the copy flips ("Welcome back, creator" and the Studio feature list on the right). Signals the context before login completes; the accent stays green for both paths.
Inline blur validation added (UX audit #19) — not visible in wireframe but spec'd.
Mobile: side panel stacks below form, same content.