FASE 4-5-6: Infraestructura, CRM, Service Orders, Notificaciones, Ahorro, Logistica, API Publica

FASE 4:
- Redis cache de stock con fallback graceful
- Multi-moneda (MXN/USD) con contabilidad en MXN
- Proveedores y ordenes de compra completo
- Meilisearch 1.5M+ partes indexadas
- Metabase KPIs con dashboard auto-generado

FASE 5:
- CRM mejorado: activities, tags, loyalty program, analytics
- Imagenes de partes: upload, resize, thumbnails WebP
- Ordenes de servicio Kanban: received->diagnosis->repair->ready->delivered
- Garantias/RMA, alertas de reorden, multi-sucursal
- Stubs BNPL (APLAZO) y ERP Sync (Aspel/Contpaqi)

FASE 6:
- Notificaciones automaticas: push/WhatsApp/email/in-app
- Reportes de ahorro vs retail_price
- Logistica + tracking: DHL, FedEx, Estafeta, 99min, Uber
- API Publica: API keys, rate limiting, catalog search

Migraciones: v1.9-v3.0
Tests: 93/93 pasando
Backup: nexus_backup_20260427_045859.tar.gz

pos/migrations/v2.0_multi_currency.sql

@@ -0,0 +1,36 @@
+-- v2.0_multi_currency.sql
+-- Mejora #8: Soporte Multi-moneda
+--
+-- Adds currency and exchange_rate columns to sales, sale_items,
+-- quotations, quotation_items, and sale_payments.
+--
+-- Business rule: inventory prices are ALWAYS in MXN (base currency).
+-- Sales can be recorded in USD (or other currencies) with conversion
+-- at checkout time. Accounting and CFDI always use MXN.
+
+-- sales
+ALTER TABLE sales
+    ADD COLUMN IF NOT EXISTS currency VARCHAR(3) DEFAULT 'MXN',
+    ADD COLUMN IF NOT EXISTS exchange_rate NUMERIC(12,6) DEFAULT 1.0;
+
+CREATE INDEX IF NOT EXISTS idx_sales_currency ON sales(currency);
+
+-- sale_items
+ALTER TABLE sale_items
+    ADD COLUMN IF NOT EXISTS currency VARCHAR(3) DEFAULT 'MXN',
+    ADD COLUMN IF NOT EXISTS exchange_rate NUMERIC(12,6) DEFAULT 1.0;
+
+-- quotations
+ALTER TABLE quotations
+    ADD COLUMN IF NOT EXISTS currency VARCHAR(3) DEFAULT 'MXN',
+    ADD COLUMN IF NOT EXISTS exchange_rate NUMERIC(12,6) DEFAULT 1.0;
+
+-- quotation_items
+ALTER TABLE quotation_items
+    ADD COLUMN IF NOT EXISTS currency VARCHAR(3) DEFAULT 'MXN',
+    ADD COLUMN IF NOT EXISTS exchange_rate NUMERIC(12,6) DEFAULT 1.0;
+
+-- sale_payments
+ALTER TABLE sale_payments
+    ADD COLUMN IF NOT EXISTS currency VARCHAR(3) DEFAULT 'MXN',
+    ADD COLUMN IF NOT EXISTS exchange_rate NUMERIC(12,6) DEFAULT 1.0;