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>

backend/src/config/db.js

@@ -0,0 +1,13 @@
+import mysql from 'mysql2/promise';
+import { env } from './env.js';
+
+export const pool = mysql.createPool({
+  host: env.db.host,
+  port: env.db.port,
+  database: env.db.name,
+  user: env.db.user,
+  password: env.db.password,
+  waitForConnections: true,
+  connectionLimit: 10,
+  dateStrings: true,
+});

backend/src/config/env.js

@@ -0,0 +1,32 @@
+import 'dotenv/config';
+
+const required = ['DB_HOST', 'DB_NAME', 'DB_USER', 'DB_PASSWORD', 'JWT_SECRET'];
+
+for (const key of required) {
+  if (!process.env[key]) {
+    if (process.env.NODE_ENV === 'production') {
+      throw new Error(`Falta la variable de entorno obligatoria: ${key}`);
+    }
+    console.warn(`[env] Falta ${key} — completa backend/.env`);
+  }
+}
+
+if (process.env.NODE_ENV === 'production' && (process.env.JWT_SECRET || '').length < 32) {
+  throw new Error('JWT_SECRET debe tener al menos 32 caracteres en producción');
+}
+
+export const env = {
+  port: Number(process.env.PORT || 4019),
+  nodeEnv: process.env.NODE_ENV || 'development',
+  db: {
+    host: process.env.DB_HOST,
+    port: Number(process.env.DB_PORT || 3306),
+    name: process.env.DB_NAME,
+    user: process.env.DB_USER,
+    password: process.env.DB_PASSWORD,
+  },
+  jwtSecret: process.env.JWT_SECRET || 'dev-only-insecure-secret',
+  jwtExpires: process.env.JWT_EXPIRES || '8h',
+  corsOrigin: process.env.CORS_ORIGIN || 'http://localhost:5196',
+  storageRoot: process.env.STORAGE_ROOT || './storage',
+};