feat: API Gateway (Express 5 + Prisma + Monday) y conexion de apps al API

- api-gateway: servicio Monday (retry 429/complejidad, paginacion cursor,
  column IDs por titulo), endpoints unidades/cotizaciones/clientes/planes,
  webhook con handshake challenge, Prisma SQLite dev, 55 tests
- cotizador: inventario desde /api/unidades con fallback a seed
- alta-clientes: POST /api/clientes + upload multipart de documentos
- cobranza: persistencia via API con respaldo offline en localStorage
- .env.example con board IDs del workspace Frasa-CAS

.env.example

@@ -0,0 +1,36 @@
+# ============================================
+# MONDAY.COM
+# ============================================
+MONDAY_API_KEY="PONER_API_KEY_DE_MONDAY"
+MONDAY_API_URL="https://api.monday.com/v2"
+MONDAY_WORKSPACE="Frasa-CAS"
+
+# Board IDs del workspace Frasa-CAS (ya creados)
+MONDAY_BOARD_CONTACTOS="18427678476"
+MONDAY_BOARD_DESARROLLOS="18427678485"
+MONDAY_BOARD_UNIDADES="18427678487"
+MONDAY_BOARD_LEADS="18427678493"
+MONDAY_BOARD_OPORTUNIDADES="18427678497"
+MONDAY_BOARD_APARTADO="18427678515"
+MONDAY_BOARD_VENTAS="18427678520"
+
+# ============================================
+# BASE DE DATOS (fase API Gateway)
+# ============================================
+DATABASE_URL="postgresql://frasa_user:CAMBIAR@postgres:5432/frasa_db?schema=public"
+POSTGRES_USER=frasa_user
+POSTGRES_PASSWORD=CAMBIAR
+POSTGRES_DB=frasa_db
+REDIS_URL="redis://redis:6379"
+
+# ============================================
+# SEGURIDAD
+# ============================================
+JWT_SECRET="cambiar_por_secreto_largo_y_aleatorio"
+JWT_EXPIRES_IN="7d"
+
+# ============================================
+# APP CONFIG
+# ============================================
+NODE_ENV=development
+PORT=3000