chore: setup design references

docs/design/screens/global.md

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+# Global states
+
+- **Route:** `any route`
+- **API:** 
+- **Visual reference:** `source/RenewCMS Screens Back-office.dc.html`, group "Global" (open it in a browser; each state is drawn at desktop and mobile, with a light/dark toggle).
+
+A 401 on any back-office call redirects to /login?redirect=<path>&reason=expired (see "Session expired" on the auth board). A 403 from an unverified account redirects to /register/pending. A 429 appears only on log in and password reset. Toasts sit bottom right on desktop and bottom center on mobile, at most 3 at once. Success and info last 5 s; errors stay until dismissed.
+
+## States
+
+### 404 inside the shell
+
+**Trigger:** An unknown route while logged in. Logged out, the same content appears inside AuthShell.
+
+- Breadcrumbs: Not found (mobile title "Not found")
+- err: {"code":"404","title":"Page not found","text":"The link may be mistyped, or the page may have moved.","primary":"Go to Home","secondary":"All articles"}
+
+### Generic error
+
+**Trigger:** An unexpected error while rendering a route.
+
+- Breadcrumbs: Home (mobile title "Home")
+- err: {"code":"Error","title":"Something went wrong","text":"This page couldn't load. Your saved work is safe. Try again, and if it keeps happening, restart the RenewCMS server.","primary":"Try again","secondary":"Go to Home"}
+
+### Offline banner
+
+**Trigger:** navigator.onLine is false. The banner is shown on every back-office page.
+
+- Breadcrumbs: Articles (mobile title "Articles")
+- offline: true
+
+### Toast stack
+
+**Trigger:** Three at most, newest at the bottom. A fourth pushes out the oldest non-error toast.
+
+- Breadcrumbs: Articles (mobile title "Articles")
+- Toast (success, circle-check): **Article published** ""Winter checklist for timber windows" is now online."
+- Toast (info, info): **That article no longer exists** "It was deleted somewhere else, so we removed it from the list."
+- Toast (error, circle-x): **Couldn't unpublish** "The server didn't respond. Nothing changed." with action "Retry"