Fix build errors: clap env feature and async borrow issues

- Enable clap "env" feature for environment variable configuration
- Enable tracing-subscriber "json" feature for structured logging
- Fix borrow checker issue in DB proxy by using Arc<Mutex> for shared write half
- Change TcpStream::split to into_split for ownership transfer

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Jonathan D.A. Jewell