Bug fixes and stability improvements.

Bug fixes and stability improvements.

New level: Search & Replace — master /, ?, n, N, *, #, and :s commands.
Redesigned exercise completion with inline results card.
Bug fixes and improvements.

4 new levels, 77 new exercises, and premium unlock.

- L4: Text Objects — diw, ciw, ci", da", ci(, di(, ci{
- L5: Visual Mode — v, V, d, y, c, ~, o
- L6: Navigation Mastery — W, B, E, F, T, ;, ,, %
- L7: Quick Edits — r, s, J, O, I, D, C, ^, ~
- One-time premium unlock for L4–L7
- Restore purchases support
- Bug fixes and exercise improvements