Discover the CLI surface via --list output

Every subcommand now exposes a --list flag that prints the command tree in machine-readable formats, with JSON and TOON outputs available alongside the default rendering. Run --list on the top-level command to enumerate all subcommands, or on any subtree (e.g. fabrik <subcommand> --list) to drill into a specific area. This gives coding agents a stable, structured way to discover available commands and options instead of parsing help prose.