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/services/subtasks.js

@@ -0,0 +1,7 @@
+import { api } from './api.js';
+
+export const listSubtasks = (activityId) => api.get(`/activities/${activityId}/subtasks`);
+export const createSubtask = (activityId, data) => api.post(`/activities/${activityId}/subtasks`, data);
+export const updateSubtask = (id, data) => api.put(`/subtasks/${id}`, data);
+export const setSubtaskDone = (id, isDone) => api.patch(`/subtasks/${id}/done`, { isDone });
+export const deleteSubtask = (id) => api.delete(`/subtasks/${id}`);