Migration 036 adds ondelete rules to 5 transitive FKs that would
otherwise block user deletion (calendar_events via calendars,
project_tasks via projects, todos via projects, etc.).
DELETE /api/admin/users/{user_id} with self-action guard, last-admin
guard, session revocation, and audit logging. Frontend gets a red
two-click confirm button in the IAM actions menu.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
