Clone-verify fixes: the HTTP request runs as base.user_admin, so set/read
x_fc_signature_image on that user (not self.env.user / uid 1); give the step a
recipe_node_id so button_finish passes the S21 no-recipe-link gate (also fixes
the pre-existing test_sign_off_finishes_step). 5/5 pass on an entech clone.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>