feat: remove Account page and add PassthroughLanding page

- Deleted the Account page and its associated logic.
- Introduced a new PassthroughLanding page for users without management access.
- Updated Settings page to conditionally display the Users link for admin users.
- Enhanced UsersPage to support passthrough user role, including invite functionality and user detail modal.
- Updated tests to reflect changes in user roles and navigation.

frontend/src/components/RequireRole.tsx

@@ -0,0 +1,25 @@
+import React from 'react'
+import { Navigate } from 'react-router-dom'
+import { useAuth } from '../hooks/useAuth'
+
+interface RequireRoleProps {
+  allowed: Array<'admin' | 'user' | 'passthrough'>
+  children: React.ReactNode
+}
+
+const RequireRole: React.FC<RequireRoleProps> = ({ allowed, children }) => {
+  const { user } = useAuth()
+
+  if (!user) {
+    return <Navigate to="/login" replace />
+  }
+
+  if (!allowed.includes(user.role)) {
+    const redirectTarget = user.role === 'passthrough' ? '/passthrough' : '/'
+    return <Navigate to={redirectTarget} replace />
+  }
+
+  return children
+}
+
+export default RequireRole