添加持续对话功能：支持每个功能模块与AI进行多轮对话和互动

feat(teacher): add reply language selector (zh/en/auto) + per-feature history (last 5); fix 4 issues: language control, history memory, 9 features layout

Add teacher agent, docs, and project updates; ClareVoiceV1 remains untracked (nested repo)