textbook-init

Use when starting a textbook project and the author wants to plan and scaffold the working directory before writing — 规划单本教材项目目录或多教材工作区，可选 git 版本管理与 README 工作说明 — e.g. "初始化教材项目"、"创建教材工作目录"、"规划教材工作区"、"建一个写教材的目录". Only creates the directory scaffold and hands off to textbook; never creates pipeline fi