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/v2.1_suppliers.sql

@@ -0,0 +1,81 @@
+-- v2.1_suppliers.sql
+-- Mejora #3: Proveedores y Órdenes de Compra
+--
+-- Adds supplier management and purchase order workflow to tenant databases.
+--
+-- Workflow:
+--   1. Create supplier (suppliers table)
+--   2. Create PO with items (purchase_orders + purchase_order_items)
+--   3. Send PO to supplier (status = 'sent')
+--   4. Receive partial or full delivery (status = 'partial' | 'received')
+--      → On receive: update stock via inventory_engine.record_purchase()
+--      → On receive: create accounting entry via record_purchase_entry()
+
+-- ═══════════════════════════════════════════════════════════════════════════
+-- SUPPLIERS
+-- ═══════════════════════════════════════════════════════════════════════════
+CREATE TABLE IF NOT EXISTS suppliers (
+    id SERIAL PRIMARY KEY,
+    name VARCHAR(200) NOT NULL,
+    contact_name VARCHAR(200),
+    phone VARCHAR(50),
+    email VARCHAR(200),
+    rfc VARCHAR(13),
+    address TEXT,
+    payment_terms VARCHAR(100),  -- e.g., "30 dias", "contado"
+    notes TEXT,
+    is_active BOOLEAN DEFAULT true,
+    created_at TIMESTAMPTZ DEFAULT NOW(),
+    updated_at TIMESTAMPTZ DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_suppliers_active ON suppliers(is_active);
+CREATE INDEX IF NOT EXISTS idx_suppliers_name ON suppliers(name);
+
+-- ═══════════════════════════════════════════════════════════════════════════
+-- PURCHASE ORDERS
+-- ═══════════════════════════════════════════════════════════════════════════
+CREATE TABLE IF NOT EXISTS purchase_orders (
+    id SERIAL PRIMARY KEY,
+    supplier_id INTEGER REFERENCES suppliers(id) ON DELETE SET NULL,
+    branch_id INTEGER REFERENCES branches(id),
+    employee_id INTEGER REFERENCES employees(id),
+    status VARCHAR(20) DEFAULT 'draft' NOT NULL,  -- draft, sent, partial, received, cancelled
+    subtotal NUMERIC(12,2) DEFAULT 0 NOT NULL,
+    tax_total NUMERIC(12,2) DEFAULT 0 NOT NULL,
+    total NUMERIC(12,2) DEFAULT 0 NOT NULL,
+    currency VARCHAR(3) DEFAULT 'MXN',
+    exchange_rate NUMERIC(12,6) DEFAULT 1.0,
+    notes TEXT,
+    supplier_invoice VARCHAR(100),
+    expected_date DATE,
+    sent_at TIMESTAMPTZ,
+    received_at TIMESTAMPTZ,
+    cancelled_at TIMESTAMPTZ,
+    created_at TIMESTAMPTZ DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_po_supplier ON purchase_orders(supplier_id);
+CREATE INDEX IF NOT EXISTS idx_po_status ON purchase_orders(status);
+CREATE INDEX IF NOT EXISTS idx_po_branch ON purchase_orders(branch_id);
+CREATE INDEX IF NOT EXISTS idx_po_created ON purchase_orders(created_at DESC);
+
+-- ═══════════════════════════════════════════════════════════════════════════
+-- PURCHASE ORDER ITEMS
+-- ═══════════════════════════════════════════════════════════════════════════
+CREATE TABLE IF NOT EXISTS purchase_order_items (
+    id SERIAL PRIMARY KEY,
+    po_id INTEGER NOT NULL REFERENCES purchase_orders(id) ON DELETE CASCADE,
+    inventory_id INTEGER REFERENCES inventory(id) ON DELETE SET NULL,
+    part_number VARCHAR(100),
+    name VARCHAR(300),
+    quantity INTEGER NOT NULL DEFAULT 1,
+    received_qty INTEGER DEFAULT 0,
+    unit_price NUMERIC(12,2) NOT NULL DEFAULT 0,
+    subtotal NUMERIC(12,2) NOT NULL DEFAULT 0,
+    notes TEXT,
+    created_at TIMESTAMPTZ DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_poi_po ON purchase_order_items(po_id);
+CREATE INDEX IF NOT EXISTS idx_poi_inventory ON purchase_order_items(inventory_id);