Cloud deployments need a way to tell readers what is happening to the
instance they are using (maintenance windows, service notices) without
shipping a release per notice.
Add a cloud.banner config block (switch, tone, dismissal, link targets and
per-language copy) and expose the resolved banner on the unauthenticated
/api/v1/system/info payload so the WebUI can render it before login. The
banner resolves to null on OSS deployments, so a self-hosted copy of
config.yaml never shows managed-service copy. Copy is plain text; only
absolute http(s) link targets are rendered.
The WebUI renders it once from the root layout, offsets the fixed app shell
and the wizard through --cloud-banner-height, and keeps a dismissal bound to
the notice it dismissed so new copy reappears.
Co-authored-by: multica-agent <[email protected]>
