chore: setup design references

docs/design/screens/boot.md

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+# App boot
+
+- **Route:** `any route, first load`
+- **API:** GET /v1/auth/me (pending)
+- **Visual reference:** `source/RenewCMS Screens Back-office.dc.html`, group "Boot" (open it in a browser; each state is drawn at desktop and mobile, with a light/dark toggle).
+
+While the session is checked, the shell renders with skeletons, never a spinner. The possible outcomes are: 200 with a verified user, which renders the route; 200 with an unverified user, which goes to /register/pending; and 401, which goes to /login?redirect=<path>. Public routes skip this check.
+
+## States
+
+### Checking session
+
+**Trigger:** The first paint on any back-office URL, and usually visible for well under a second.
+
+- Breadcrumbs: Home (mobile title "Home")
+- boot: true