Restructure english branch: replace old translations with latest English content

- Replace old English-named directories with Chinese-named directories from master
- Convert all articles to English using tutorial source translations (Java code, --lang en)
- Rename all directories and files to English names
- Convert internal links to https://labuladong.online/en/algo/ format
- Regenerate README with English intro and full TOC from tutorial SUMMARY.md
- Add website screenshot