chore: estructura inicial del MVP

Backend (Express + MariaDB) y frontend (React + Vite, identidad Fluent/Windows) con el
nucleo funcional: seguridad, organizacion, proyectos, actividades, subtareas, dependencias,
dashboard, calendario, gantt, comentarios, adjuntos, notificaciones in-app y catalogos.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/components/Expander.jsx

@@ -0,0 +1,19 @@
+import { useState } from 'react';
+import { ChevronRight } from 'lucide-react';
+
+export function Expander({ icon: Icon, title, description, defaultOpen = false, children }) {
+  const [open, setOpen] = useState(defaultOpen);
+  return (
+    <div className={`expander ${open ? 'open' : ''}`}>
+      <div className="expander-header" onClick={() => setOpen((v) => !v)}>
+        {Icon && <Icon size={18} />}
+        <div>
+          <div className="expander-title">{title}</div>
+          {description && <div className="expander-desc">{description}</div>}
+        </div>
+        <ChevronRight className="chevron" size={16} />
+      </div>
+      {open && <div className="expander-body">{children}</div>}
+    </div>
+  );
+}