Build GitHub Pages homepage and detailed docs

[fangpin]

Summary

• build a bilingual GitHub Pages homepage for redis-rs with a prominent GitHub link and a clearer top-level docs entry
• add a dark just-the-docs theme override so detailed docs match the homepage visual system
• expand the implementation docs into finer-grained English and Chinese chapters for runtime, protocol, storage, RDB, replication, command execution, and streams/transactions

Test Plan

• cargo test
• bundle 2.5.9 exec jekyll build --baseurl "/redis-rs"
• verified local preview routes for homepage, docs overview, server-runtime, and zh docs overview return 200