Sell the admin GUI in its README (screenshot, purpose, modes)

[zeevdr]

Description

The admin GUI README is a developer setup document (npm install, env vars, customization) with no screenshot or gif. For a graphical product, the absence of any image is the biggest single miss in our README set — the most demo-able thing we have is invisible. The genuinely differentiating capabilities are buried as env-var documentation: layout modes (full, single-schema, single-tenant — the embed story) and feature toggles plus white-labeling via labels.json / theme.json (the "hand a safe UI to non-engineers" story).

Why this blocks beta

A GUI that can't be seen doesn't convert. Before beta, the UI README should show what it looks like and lead with who it's for, not how to run the dev server.

Acceptance criteria

• A screenshot or short gif of the running UI appears near the top (schema browser / config editor / audit view)
• A one-to-two line "what it's for" lead sits above the Development section (a browser UI to hand to product/ops to change config safely, embeddable into internal tools)
• Layout modes and feature toggles are promoted into a short "Embedding and white-labeling" section that frames the use case (restrict non-developers from editing schemas, rename concepts per domain, hide features) — not just listed as config keys
• Dev setup and the env-var reference are retained but placed below the pitch

References

• decree-ui/README.md (whole file); customization :40-87, layout modes :36
• Screenshot source: reuse or capture from the Playwright / e2e stack