Function norm

public/js/fileDragDrop.js:319–322

    // optional: mirror PHP self/descendant guard so we fail fast
    const norm = s => {
      if (!s) return '';
      return s.replace(/^[/\\]+|[/\\]+$/g, '');
    };
    const srcNorm = norm(source);
    const dstNorm = destination === 'root' ? '' : norm(destination);