refactor: remove security-related hooks and pages

- Deleted `useSecurity.ts` hook which managed authentication users, providers, and policies.
- Removed `Policies.tsx`, `Providers.tsx`, and `Users.tsx` pages that utilized the above hook.
- Cleaned up the `index.tsx` file in the Security section to remove references to the deleted pages.
- Updated mock data by removing unused properties related to forward authentication.

frontend/src/components/__tests__/ProxyHostForm.test.tsx

@@ -234,25 +234,4 @@ describe('ProxyHostForm', () => {
 
     expect(screen.getByLabelText(/Domain Names/i)).toHaveValue('my-app.existing.com')
   })
-
-  it('toggles forward auth fields', async () => {
-    renderWithClient(
-      <ProxyHostForm onSubmit={mockOnSubmit} onCancel={mockOnCancel} />
-    )
-
-    // The Forward Auth toggle now uses "Enable External Forward Auth" label
-    // and only appears when no Access Policy is selected (default is no policy)
-    const toggle = screen.getByLabelText('Enable External Forward Auth')
-    expect(toggle).not.toBeChecked()
-
-    // Bypass field should not be visible initially
-    expect(screen.queryByLabelText('Bypass Paths (Optional)')).not.toBeInTheDocument()
-
-    // Enable it
-    fireEvent.click(toggle)
-    expect(toggle).toBeChecked()
-
-    // Bypass field should now be visible
-    expect(screen.getByLabelText('Bypass Paths (Optional)')).toBeInTheDocument()
-  })
 })