fix: asegurar runtime android y diagnostico pos

openspec/changes/fix-android-webview-runtime/specs/android-webview-runtime/spec.md

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+# Spec Delta
+
+## Purpose
+
+Garantiza que la versión Android muestre los controles de navegación y operación con iconos visibles y que los errores de venta puedan resolverse desde la interfaz.
+
+## ADDED Requirements
+
+### Requirement: Iconos y menú operables
+The system SHALL render MDI icons for navigation, quantity controls, deletion, and breadcrumbs in the Android WebView.
+
+#### Scenario: Menú APK
+- **WHEN** the app opens on Android
+- **THEN** a visible menu button opens the navigation drawer
+- **AND** breadcrumb and action icons are visible
+
+### Requirement: Diagnóstico de stock
+The system SHALL show available stock and explain when a product cannot be added or sold because inventory is insufficient.
+
+#### Scenario: Producto sin inventario
+- **WHEN** user selects a product with zero stock
+- **THEN** the product is not added to the cart
+- **AND** the UI explains that initial inventory must be registered