refactor: resolve Live Share visitor locations offline

[Mazha0309]

Summary

• replace the optional Baidu IP geolocation request with bundled offline ip2region lookup
• stop sending visitor IP addresses to any external geolocation service
• return country, province, city, and ISP with a bounded in-memory cache
• remove BAIDU_MAP_AK configuration and update the Live Share detail schema to v4
• bump the server version to 0.8.1

Validation

• npm run verify (168 server tests, 22 Web tests)
• dist HTTP/database smoke test
• bundled database lookup test