v0.31.0: Faster reads, better UX, fewer bugs v0.31.0

Shipped ranged reads for snappier performance, fixed that bottom border colour that's been bugging everyone, and added some quality-of-life wins like Alt+D for forward word deletion and a --resume hint when you exit. Also locked down tool output masking with proper behavioral tests and cleaned up the preflight docs so you're not guessing what to do next. Nothing groundbreaking, just solid stuff that makes the CLI actually nicer to use.