message: allow pill-candidate parts in commands
diff: @@ -163,10 +163,7 @@ export default class SendMessageComposer extends React.Component {
  _isSlashCommand() {
  const parts = this.model.parts;
  - const isPlain = parts.reduce((isPlain, part) => {
  - return isPlain && (part.type === "command" || part.type === "plain" || part.type === "newline");
  - }, true);
  - return isPlain && parts.length > 0 && parts[0].text.startsWith("/");
  + return parts.length && parts[0].type === "command";
  }
  async _runSlashCommand() {
  