rich-click CLI: --output json for machine-readable help

[ewels]

Stacked on top of #331 (base branch help-json). Implements dwreeves's CLI suggestion from that review.

What

Extends the rich-click CLI's --output option with a json value, so machine-readable help works through the CLI wrapper for any Click CLI — even ones that haven't opted into help_json.

$ rich-click --output=json flask --help
{ "name": "flask", "path": "flask", ... }

Two behaviours:

1. rich-click --output=json [cmd] --help emits the --help-json schema instead of rendered help. A plain --help yields JSON — no need for the target to enable help_json. Implemented via a RichCommand.get_help() override that returns get_help_json() when the context's export_console_as is "json".
2. --output applies to the --help-json flag too. The schema is rendered through the recording console and exported, so rich-click -c '{"help_json": true}' --output=svg [cmd] --help-json produces an SVG of the JSON (dwreeves's second case).

Why --output json, not --json

It's a value of the existing -o/--output option, not a new flag. The wrapper consumes --output before the script args (allow_interspersed_args=False), so the wrapped command never sees it — no risk of clashing with the target's own options.

Notes

• getvalue() treats "json" as plain-text export defensively; it should never reach there for help, since get_help short-circuits.
• Docs updated (rich_click_cli.md, cross-ref from machine_readable_help.md); 3 new tests + regenerated --help snapshot.

⚠️ Review/merge #331 first — this is stacked on it, so the diff will look correct once the base lands on main.

[dwreeves]

FWIW, you could do --json if you wanted, the allow_interspersed_args=False thing makes any options you add before the script_and_args argument safe to add, so there is no technical limitation, it's just an API design choice. And maybe that's the correct API design choice? I don't know!!! 😅 I didn't consider it when I proposed adding this. I see the argument for it being that --output is a decision for rendering, whereas --json fundamentally changes the help text path. So it could be the correct API decision. What do you think?

[ewels]

I guess one benefit of --json would be that this example gets simpler:

rich-click -c '{"help_json": true}' --output=svg [cmd] --help-json

instead becoming this?

rich-click --json --output=svg [cmd] --help

I'm not sure I have a strong preference either way. Honestly I can't see many people saving SVGs of JSON output, so combination of the two probably isn't a common scenario 😅