Drive a running Neovim for screenshots via its RPC socket

To stage README screenshots of a Neovim config, launch it in a terminal, then control that instance through its auto-created server socket ($XDG_RUNTIME_DIR/nvim.<embed-pid>.0; with the nix wrapper the socket belongs to the --embed child, not the TUI process). nvim --server <sock> --remote-send '<Space>e' does not fire leader mappings when which-key intercepts the leader. Call the Lua directly through --remote-expr luaeval(...) instead, e.g. require('snacks').picker.explorer(). On compositors without focus-by-app-id IPC, a newly spawned terminal may not take focus. Check the focused window before sending a fullscreen toggle, or you fullscreen the wrong app, and full-screen captures can leak private windows.