Two bugs surfaced by Excel import on a lesson with a lesson_path column:
1. resolveLesson created lessons without owner_id, so after the ownership
model (sub-project B) they never appeared in getLessonTree — import
reported success but nothing was visible.
2. lesson_path was resolved at the root; cards landed in new root lessons
instead of under the lesson the import was started from.
Now: auto-created lessons get ownerId + visibility 'private'; lesson_path is
resolved relative to the started lesson (each segment a sublesson). Also drop
the stale eager card_progress insert (progress is per-user and lazy since B).
