Toolbar widgets

A placement may render an input instead of a button. It reads its value from a source and emits an event on validation — the store is still only written by a handler.

ctx.place({
  id: "title",
  toolbar: "view:notes:editor",
  order: 5,
  widget: {
    valueType: "text",
    label: ctx.i18n.key("widget.title"),
    width: "w-48",
    event: "notes/document.rename",     // payload: { value, context }
    value: valueFrom(slice, (state, context) => targetDoc(context, state)?.title ?? ""),
    // commitOn: "change" to emit on every keystroke; default is Enter / blur
  },
});