fix(config, cli): Render shell commands correctly in user output

[JeanMertz]

A command configured with shell = true rendered with a newline in the middle of it and a quote on the wrong side of the space, so the label confirmation prompt broke across two lines and showed /bin/sh -c' before the command itself. It now reads sh -c 'git rev-parse --show-toplevel', and arguments are shell-quoted so a multi-word argument stays one token instead of looking like two. Every message that names a command picks this up: label prompts and failures, tool spawn errors, and custom parameter formatter errors.

JP also logs an INFO line naming the editor it is about to open, so a trace shows which program was handed the terminal:

{"message":"Opening configured editor.","editor":"nvim"}

Without it, an editor that exits without touching the draft is indistinguishable from a user who saved an empty file. A conversation carrying editor.cmd = "true" from a non-interactive run drops every query as empty and says nothing about why.

CommandConfig splits the two jobs its Display was serving. shell_command_line returns the string passed to sh -c, and is what the editor, tool, and label executors call; Display is the readable form, distinct enough now that spawning through it would fail visibly rather than work by accident until the two drifted apart.