- Add migrate_to_workspace() function to sync.py that copies flat notes to workspace directories
- Extract ## 🔍 精读 section into deep-reading.md in workspace
- Create ai/ directory in each paper workspace
- Wire migration into run_index_refresh() before build_index()
- Update _build_entry() in asset_index.py to write notes to workspace path when workspace dir exists
- Preserve flat path fallback for backward compatibility when workspace dir does not exist