A plain module-level singleton store (banner.ts) plus a single renderer
(BannerStack, mounted once above LoginGate in main.tsx) -- no React
Context, since this codebase has none today and a plain exported
function is callable from anywhere, including api/client.ts (a plain
module, not a component) in a later task. Nothing calls it yet; that's
each of this plan's remaining tasks.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
