devenv 2.1: Nix with zsh, fish, and nushell via libghostty
Summary
Devenv 2.1 adds native support for zsh, fish, and nushell via libghostty, enabling per-shell rcfile generation, environment diff tracking, and prompt integration. It replaces direnv-based activation with automatic activation hooks and introduces OpenTelemetry tracing for better observability. The update focuses on multi-shell developer experience and improved process management for coding agents.