feat: Improve Supplier wizard with delivery days and optional payment terms

Supplier Wizard Improvements:
- Added 'Días de Entrega' (Lead Time Days) field - CRITICAL field
- Field shows as required with asterisk and helper text
- Validates that lead time is provided before allowing continue
- Made 'Términos de Pago' optional (not critical info)
- Added empty option 'Seleccionar...' to payment terms dropdown
- Updated API call to include lead_time_days parameter
- Payment terms now sends undefined if not selected
- Lead time days properly parsed as integer before sending to API

These changes ensure critical logistics information is captured while
making optional business terms more flexible.

frontend/src/components/domain/unified-wizard/wizards/SupplierWizard.tsx

@@ -18,7 +18,8 @@ const SupplierInfoStep: React.FC<WizardDataProps> = ({ data, onDataChange, onNex
     phone: data.phone || '',
     email: data.email || '',
     address: data.address || '',
-    paymentTerms: data.paymentTerms || 'net30',
+    paymentTerms: data.paymentTerms || '',
+    leadTimeDays: data.leadTimeDays || '',
     notes: data.notes || '',
   });
 
@@ -107,13 +108,29 @@ const SupplierInfoStep: React.FC<WizardDataProps> = ({ data, onDataChange, onNex
 
           <div>
             <label className="block text-sm font-medium text-[var(--text-secondary)] mb-2">
-              Términos de Pago
+              Días de Entrega *
+              <span className="ml-1 text-xs text-[var(--text-tertiary)]">(Tiempo de lead time)</span>
+            </label>
+            <input
+              type="number"
+              value={supplierData.leadTimeDays}
+              onChange={(e) => setSupplierData({ ...supplierData, leadTimeDays: e.target.value })}
+              placeholder="Ej: 7"
+              min="0"
+              className="w-full px-3 py-2 border border-[var(--border-secondary)] rounded-lg focus:outline-none focus:ring-2 focus:ring-[var(--color-primary)]"
+            />
+          </div>
+
+          <div>
+            <label className="block text-sm font-medium text-[var(--text-secondary)] mb-2">
+              Términos de Pago (Opcional)
             </label>
             <select
               value={supplierData.paymentTerms}
               onChange={(e) => setSupplierData({ ...supplierData, paymentTerms: e.target.value })}
               className="w-full px-3 py-2 border border-[var(--border-secondary)] rounded-lg focus:outline-none focus:ring-2 focus:ring-[var(--color-primary)]"
             >
+              <option value="">Seleccionar...</option>
               <option value="immediate">Inmediato</option>
               <option value="net30">Neto 30 días</option>
               <option value="net60">Neto 60 días</option>
@@ -139,7 +156,7 @@ const SupplierInfoStep: React.FC<WizardDataProps> = ({ data, onDataChange, onNex
       <div className="flex justify-end pt-4 border-t border-[var(--border-primary)]">
         <button
           onClick={handleContinue}
-          disabled={!supplierData.name || !supplierData.phone}
+          disabled={!supplierData.name || !supplierData.phone || !supplierData.leadTimeDays}
           className="px-6 py-2.5 bg-[var(--color-primary)] text-white rounded-lg hover:bg-[var(--color-primary)]/90 disabled:opacity-50 disabled:cursor-not-allowed transition-colors"
         >
           Continuar
@@ -216,7 +233,8 @@ const ProductsPricingStep: React.FC<WizardDataProps> = ({ data, onDataChange, on
         email: data.email || undefined,
         phone: data.phone,
         address: data.address || undefined,
-        payment_terms: data.paymentTerms || 'net30',
+        payment_terms: data.paymentTerms || undefined,
+        lead_time_days: data.leadTimeDays ? parseInt(data.leadTimeDays) : undefined,
         tax_id: undefined,
         notes: data.notes || undefined,
         status: 'active',