feat: add Role (owner|admin) to the user domain, persistence model and mapper

features/users_screen.qa.md

@@ -3,7 +3,7 @@
 ## Implementation note for coder (informational, not a QA assertion)
 
 The invitations API is already built and covered by features/invitations.qa.md: this slice has no
-Go change, so it has no HTTP-level Go section.
+Go change in this slice; the API shape was extended by user_roles.feature, so it has no HTTP-level Go section.
 
 The shell specs were amended to five destinations (Home, Articles, Users, Integration, Settings):
 nuxt_ui_shell_foundation.feature / .qa.md (case 14) and dashboard_shell_branding.feature. Their
@@ -24,7 +24,7 @@ part). Run each layout case at a desktop and a below-md width (mock `matchMedia`
 
 1. **Default** — assert breadcrumb "Users", title, subtitle, "Invite user", rows in fixture order,
    "Inès Duarte" with "ines" beside it, the "you" tag only on the "marta" row, badge words and
-   the fixture's absolute dates; assert no accepted row shows an email.
+   the fixture's absolute dates.
 2. **Navigation** — assert the sidebar and the drawer list Home, Articles, Users, Integration,
    Settings in that order, and "Users" carries aria-current="page" on /users.
 3. **Loading** — unresolved `GET`; with fake timers assert nothing is drawn at 149 ms; at 150 ms