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/hooks/__tests__/useAuth.test.tsx

@@ -15,7 +15,7 @@ describe('useAuth hook', () => {
   })
 
   it('returns context inside provider', () => {
-    const fakeCtx = { user: { user_id: 1, role: 'admin', name: 'Test', email: 't@example.com' }, login: async () => {}, logout: () => {}, changePassword: async () => {}, isAuthenticated: true, isLoading: false }
+    const fakeCtx = { user: { user_id: 1, role: 'admin' as const, name: 'Test', email: 't@example.com' }, login: async () => {}, logout: () => {}, changePassword: async () => {}, isAuthenticated: true, isLoading: false }
     render(
       <AuthContext.Provider value={fakeCtx}>
         <TestComponent />