The Brain > Add tab rendered only a text input and category select with no
submit control, and Enter submission relied on a deprecated keypress
listener that is not guaranteed to fire, so the form could not be
submitted at all (#5828).
Add a labelled submit button styled like the neighbouring Skill Import
button (theme-io-btn, inline SVG icon), switch the Enter handler to
keydown with preventDefault, ignore IME composition, and pin both submit
paths with a source-level regression test.
Fixes#5828
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
