fix: migrate README CDN images + clean China-only references + Algolia cleanup #208

What was done

1. README.md CDN migration (4 images)

All cdn.paicoding.com images in README.md migrated to self-hosted CDN (raw.githubusercontent.com/acailic/javasi-cdn/master/):

• logo.png (uploaded to javasi-cdn repo)
• tobebetterjavaer-map.png (already existed)
• stutymore/README-20241106103513.png (uploaded)
• stutymore/README-20230829162301.png (uploaded)

2. README.md China-only reference cleanup

• Removed old domain link tobebetterjavaer.com
• Removed paicoding.com/column/5/1 (Jishupai column)
• Removed Gitee link (China-only platform)
• Badge links redirected javabetter.cn -> javasi.dev
• GitHub links redirected itwanger/toBeBetterJavaer -> acailic/toBeBetterJavaer
• VuePress Theme Hope link fixed from /zh/ to English version
• Paicoding friendly-link shortened (removed Jishupai reference)

3. Algolia docsearch comment cleanup in theme.ts

Stale reference to tobebetterjavaer Algolia index replaced with clear comment that local search is enabled automatically.

Remaining

• 124 external links to Chinese platforms (bilibili, zhihu, csdn) in docs/src/ are reference links in articles, not monetization — they stay
• Build verification and deploy