Delete questionnaire templates as the Retraced admin

Permanently deletes the given questionnaire templates. All-or-nothing: every id must belong to the calling company and be a template, and none may be Retraced-owned unless the caller is a Retraced admin — otherwise nothing is deleted. The rows are removed rather than flagged, and their sections and questions are orphaned rather than deleted, as in the legacy route. The tenant twin is DELETE /api/questionnaires/templates; this one is guarded on the admin right instead.