docs(roadmap): fold activity-management UI port into Phase 3 scope

docs/roadmap.md

@@ -175,8 +175,14 @@ Each phase keeps the system working and is its own spec → plan → build cycle
   `/api/admin/sessions`. Public sign-up is closed; activity writes are admin-only.
   _Done when:_ workers see only their own sessions; an admin account exists.
 - **Phase 3 — Admin panel.** The React admin app: live active-work view, reports/export,
-  user management, **manual entry/edit (the fallback)**. _Done when:_ an admin can see
-  who's working now, manage users, and hand-correct a session.
+  user management, **activity management**, **manual entry/edit (the fallback)**.
+  Activity management (add/edit/delete handelingen + their `insole_types`) was removed from the
+  worker client in the Phase 2 follow-up because it is admin-only; it must be **ported here**. The
+  backend already exists (`/api/activities` writes are admin-gated; `useActivities`/the legacy
+  worker `Settings.tsx` at git `decb158`/`1631c16` are the UI reference), so this is a UI-only port.
+  User management likewise consumes the existing better-auth `/api/auth/admin/*` endpoints, and the
+  live view + reports consume `/api/admin/sessions[/active]`. _Done when:_ an admin can see who's
+  working now, manage users **and activities**, and hand-correct a session.
 - **Phase 4 — Workbench scanning.** QR at the bench → select workbench/activity, with
   manual selection fallback. _Done when:_ scanning a bench QR pre-fills the session.
 - **Phase 5 — Polish & deploy.** Reporting niceties, dependency slimming, push the