webclient: make the protocol proposal card a document, not a kit tile ...

GnCard is a 340px tile with an uppercased title and GnSteps uppercases
every step, so a protocol document came out as a narrow column of caps with
its body shown as raw markdown. The card is a chat domain card now: an
app-owned full-width frame (accented left edge for pending/accepted/
rejected) with the kit's buttons, alert, chips, badge and loader.

- shows what was missing: when to use it (triggers), preconditions, steps
  with their action and check, post-checks, and the body as rendered
  markdown under "Context";
- unwraps a step the model wrote as a YAML mapping, which the parser turns
  into Python repr text, so the step reads instead of leaking {'id': ...};
- says "Add to catalog" and shows an "In the catalog" badge once decided.