swarm-ui: the terminal message box has a placeholder and a spinner instead of a label and a sent line

The label 'message <agent>' is the input's placeholder (the label stays for
screen readers). The send button shows a spinner over its label while the
request is pending and keeps its width, and the 'sent' line is gone: the box
empties when the message is held. Spinner is a component of its own now, used
by the button and the refresh picker.

frontend/packages/swarm-ui/src/ui/text-field/TextField.tsx

@@ -22,6 +22,7 @@ export function TextField({
   title,
   required,
   placeholder,
+  hideLabel,
   suggestions,
 }: {
   id: string;
@@ -33,13 +34,15 @@ export function TextField({
   title?: string;
   required?: boolean;
   placeholder?: string;
+  /** The label is for assistive tech only; the placeholder says it on screen. */
+  hideLabel?: boolean;
   /** Values to pick from. The field stays free text: a value that is not in
    * the list can still be typed. */
   suggestions?: TextFieldSuggestion[];
 }) {
   const listId = `${id}-suggestions`;
   return (
-    <FormField label={label} htmlFor={id}>
+    <FormField label={label} htmlFor={id} hideLabel={hideLabel}>
       <input
         id={id}
         class="ui-form-control"