refactor: 将课程各步骤拆分到 features/lesson/steps/

lesson_flow.dart 保留流程状态、公共脚手架与小组件,预习/听/说/读/写/独立表达
六个步骤各自成为 part 文件。代码仅搬移并经 dart format 格式化,无用户可见变化。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
shenlei
2026-09-16 17:23:26 +09:00
co-authored by Claude Opus 5
parent 8302977351
commit be70ad2a29
7 changed files with 1097 additions and 1025 deletions
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