Studio Design tab: a component explorer and a live theme editor; themes compile to edge-served CSS that updates every app on the theme in real time #6297

Owner, 2026-10-26: "the studio page in the forge could have a component library explorer… open-platform has a really cool system for styling, where the CSS is compiled and placed at the edge so you can update any apps that reference that theme in real time. This would be a fantastic interface for the studio page. Give designers the ability to adjust themes right in the forge, and they reflect in real time."

Done when:

• The studio gets a Design tab: the component explorer (#5817 gallery, #6009 registry items) beside a theme editor.
• Themes are data: design tokens (color roles for light and dark, type scale, radii, spacing, motion), stored per org or app, with history and undo (fleet ops).
• Compiled at the edge, live: saving a theme compiles it to a versioned CSS file (custom properties) served at a stable URL, e.g. /_theme/<org>/<name>.css, the way open-platform's brand CSS reaches every app. Apps reference the URL instead of bundling colors, so every app on that theme updates in real time: open pages re-fetch through a push on change, with no redeploy.
• The editor previews before you publish:

- The gallery and a few real apps render live against the draft (side by side: current and draft, light and dark). - A contrast check blocks a palette that fails WCAG AA. - Publish is one click, with Revert right there.

• Who can edit: the designer role (#6286) and org admins. Every change is attributed.
• First pull: tokens for the forge's own theme, served as /_theme/forge.css, with one app switched to load it, and a change appearing in an open page within 2 s.

Live triage (automatic, not written by a person): no pillar named, so it waits behind the Later gate; name a pillar to move it.