Replace positional args[3..5] assertions with assert_called_once_with using
rounding=/thickness=/flags= kwargs to match the existing add_rect call in
src/theme_nerv_fx.py:AlertPulsing.render and the parallel test in
tests/test_theme_nerv_fx.py:TestThemeNervFx.test_alert_pulsing_render.
Fixes test_alert_pulsing_render_active IndexError that surfaced when the
positional contract was asserted against the kwargs-shaped production call.
ed