feat: rewrite frontend auth — roles from org store, Logto org role names

Replace ID-token claim reads with org store lookups in useAuth and
usePermissions; add currentOrgRoles to useOrgStore; update role names
to Logto org role conventions (admin/member); remove username from
Layout (no longer derived from token claims).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/components/Layout.tsx

@@ -100,7 +100,7 @@ function PlatformIcon() {
 
 export function Layout() {
   const navigate = useNavigate();
-  const { username, logout, isPlatformAdmin } = useAuth();
+  const { logout, isPlatformAdmin } = useAuth();
 
   const [envSectionOpen, setEnvSectionOpen] = useState(true);
   const [collapsed, setCollapsed] = useState(false);
@@ -166,7 +166,7 @@ export function Layout() {
         {/* User info + logout */}
         <Sidebar.FooterLink
           icon={<UserIcon />}
-          label={username ?? 'Account'}
+          label="Account"
           onClick={logout}
         />
       </Sidebar.Footer>
@@ -177,7 +177,7 @@ export function Layout() {
     <AppShell sidebar={sidebar}>
       <TopBar
         breadcrumb={[]}
-        user={username ? { name: username } : undefined}
+        user={undefined}
         onLogout={logout}
       />
       <Outlet />