feat: mejorar pos movil y cierre de jornada

openspec/changes/improve-mobile-pos-closing/specs/mobile-pos-flow/spec.md

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+# Spec Delta
+
+## Purpose
+
+Permite vender cómodamente desde celulares mostrando el carrito, la búsqueda de productos y la devuelta sin obligar a recorrer una lista larga.
+
+## ADDED Requirements
+
+### Requirement: Catálogo compacto en POS
+The system SHALL keep the cart visible and allow selecting products through a searchable compact list or dialog.
+
+#### Scenario: Selección en móvil
+- **WHEN** user opens Ventas on a narrow viewport
+- **THEN** the cart and total remain visible
+- **AND** user can search and add a product from the catalog dialog
+
+### Requirement: Calcular devuelta
+The system SHALL calculate and display change for cash payments before saving a sale.
+
+#### Scenario: Pago en efectivo
+- **GIVEN** sale total is 12000
+- **WHEN** user enters 20000 as received cash
+- **THEN** the UI displays change of 8000
+- **AND** the sale can be confirmed
+
+#### Scenario: Efectivo insuficiente
+- **WHEN** received cash is below the sale total
+- **THEN** confirmation is disabled and an actionable message is shown