form_errors are not displayed

WTForms [form_errors](https://wtforms.readthedocs.io/en/3.0.x/forms/#wtforms.form.Form.form_errors) are form-wide (non-field) error messages

These are not displayed by `render_form()`

An example, say you wanted to validate that username and password are not the same...this would be a form-error and not an error specific to a given field

Could add something like this near the top of the form:

{% if form.form_errors %}