refactor(rpiv-ask-user-question): move the Submit-tab note hint below the picker

The `n to add a note` affordance rendered as a standalone dim row wedged
between the submit prompt and its picker, breaking the prompt-to-options
reading flow, and a committed note left no trace once the editor closed.
The hint now lives in a bottom key-hint row below the picker
(buildSubmitHintText, the same middot-joined idiom as the question tabs'
buildHintText — while the editor is open the note part gives way to the
Shift+Enter newline hint), and the committed note renders as a `Note`
entry in the review list, hidden while the editor is the live surface.
footerRowCount stays 5; the hint row gains the sibling paddingLeft. One
new locale key (review.note_label), docs and CHANGELOG updated;
docs/submit-tab.jpg still shows the old layout and needs a fresh capture.