ZhaoZeW/dsh-rollback

TRAE-style conversation rollback rebuilt for DSH 0.1.7-rc.2: per-turn file checkpoints restore touched files and truncate the model context in place under the same session id. Adds a /rollback doctor framework-contract self-check, an affected-file diff preview computed against the current on-disk state so it stays correct after a restart, a one-click undo-last action with a Ctrl+Shift+Z shortcut, a setting for whether rolled-back messages stay hidden, and English UI text.