v0.4.1

Content quality pass + a new in-drill option.

• Every challenge vetted, challenge by challenge — buffers scale-matched to the technique (:sort on 10-line lists, :g/block-range on scattered lines, marks on real multi-line code), solutions re-derived and verified through real vim.
• Dropped the junk — toy/abstract buffers, whimsical prose, contrived solutions, near-duplicates, and an off-skill example. 549 → 222 challenges, ~4 per skill, all 61 lessons kept.
• Tighter in-vim text — every why/hint trimmed to fit the goal pane.
• New: turn a lesson off mid-drill — press o on the result screen to switch the current skill off so it stops coming up (re-enable in Settings ▸ Lessons).