v0.4.0

• yank challenges graded on the unnamed register, not the buffer
• key remaps for any key in any mode (escape aliases folded in); lessons whose taught key you remapped are warned and hidden
• free-form, endless, no-repeat blind-all sweep; Blind names the expected technique
• Grind lets you pick the skill (menu, or --reps N --skill ID)
• spaced repetition graded by efficiency — fast solves promote and rest longer, slow-but-correct holds, a miss demotes (one slip at the top forgiven)
• fix the keystroke count when Enter sends (Ctrl-J) instead of