feat: MercadoLibre integration + inventory bulk publish + WhatsApp bridge fixes

- Add MercadoLibre OAuth, listings, orders, webhooks and category search
- New marketplace_external_bp.py, meli_service.py, marketplace_external_service.py
- New marketplace_external.html/js with ML management UI
- Inventory: bulk publish to ML with category autocomplete, listing type and shipping selectors
- Inventory: new .btn--meli styles, select/label CSS fixes
- WhatsApp bridge: rate limiting, 440/515/408 error handling, stale watchdog
- DB migration v3.4_meli_integration.sql for marketplace_listings, orders, sync_queue
- Add Celery tasks for ML sync and webhook processing
- Sidebar: MercadoLibre navigation link

pos/static/js/pos.js

@@ -123,6 +123,8 @@ const POS = (() => {
                 currentRegister = null;
                 document.getElementById('registerInfo').innerHTML =
                     '<span style="color:var(--color-error);cursor:pointer;" onclick="POS.showOpenRegisterModal()" title="Clic para abrir caja">&#x26A0; Sin caja abierta — Clic para abrir</span>';
+                // Force open register modal on first load
+                showOpenRegisterModal();
             }
         } catch (e) {
             console.warn('Register check failed:', e);
@@ -253,6 +255,9 @@ const POS = (() => {
             discount_pct: parseFloat(item.discount_pct || 0),
             tax_rate: parseFloat(item.tax_rate || 0.16),
             stock: item.stock || 0,
+            price_1: parseFloat(item.price_1 || 0),
+            price_2: parseFloat(item.price_2 || 0),
+            price_3: parseFloat(item.price_3 || 0),
         });
 
         renderCart();
@@ -265,6 +270,67 @@ const POS = (() => {
         renderCart();
     }
 
+    function clearCart() {
+        cart.length = 0;
+        selectedRow = -1;
+        renderCart();
+    }
+
+    function openCancelModal() {
+        const overlay = document.getElementById('overlay-cancelar-venta');
+        const dialog = document.getElementById('modal-cancelar-venta');
+        if (overlay) overlay.classList.add('active');
+        if (dialog) dialog.classList.add('active');
+    }
+
+    function closeCancelModal() {
+        const overlay = document.getElementById('overlay-cancelar-venta');
+        const dialog = document.getElementById('modal-cancelar-venta');
+        if (overlay) overlay.classList.remove('active');
+        if (dialog) dialog.classList.remove('active');
+    }
+
+    function changeQuantity() {
+        if (selectedRow < 0 || selectedRow >= cart.length) {
+            showToast('Selecciona un articulo primero', 'warn');
+            return;
+        }
+        const q = prompt('Nueva cantidad:', cart[selectedRow].quantity);
+        if (q !== null) {
+            const n = parseInt(q);
+            if (n > 0) {
+                cart[selectedRow].quantity = n;
+                renderCart();
+            }
+        }
+    }
+
+    function applyDiscount() {
+        if (selectedRow < 0 || selectedRow >= cart.length) {
+            showToast('Selecciona un articulo primero', 'warn');
+            return;
+        }
+        const d = prompt('Descuento %:', cart[selectedRow].discount_pct);
+        if (d !== null) {
+            const n = parseFloat(d);
+            if (n >= 0 && n <= 100) {
+                cart[selectedRow].discount_pct = n;
+                renderCart();
+            }
+        }
+    }
+
+    // Wire confirm-cancel button
+    document.addEventListener('DOMContentLoaded', function() {
+        var btn = document.getElementById('btnConfirmCancel');
+        if (btn) {
+            btn.addEventListener('click', function() {
+                clearCart();
+                closeCancelModal();
+            });
+        }
+    });
+
     function renderCart() {
         const tbody = document.getElementById('cartBody');
         const table = document.getElementById('cartTable');
@@ -472,6 +538,9 @@ const POS = (() => {
             cost: item.cost,
             tax_rate: item.tax_rate,
             stock: item.stock,
+            price_1: item.price_1,
+            price_2: item.price_2,
+            price_3: item.price_3,
         });
         hideSearchResults();
         document.getElementById('itemSearch').value = '';
@@ -530,11 +599,22 @@ const POS = (() => {
         }
     }
 
+    function recalcCartPrices() {
+        const tier = currentCustomer ? (currentCustomer.price_tier || 1) : 1;
+        cart.forEach(item => {
+            if (item.price_1 > 0) {
+                item.unit_price = tier === 3 ? item.price_3 : tier === 2 ? item.price_2 : item.price_1;
+            }
+        });
+    }
+
     async function selectCustomer(customer) {
         currentCustomer = customer;
         document.getElementById('customerAutocomplete').style.display = 'none';
         document.getElementById('customerSearchWrap').querySelector('input').style.display = 'none';
 
+        recalcCartPrices();
+
         const tiers = { 1: 'P1 Mostrador', 2: 'P2 Taller', 3: 'P3 Mayoreo' };
         document.getElementById('customerName').textContent = customer.name;
         document.getElementById('customerTier').textContent = tiers[customer.price_tier] || 'P1';
@@ -1255,7 +1335,7 @@ const POS = (() => {
     init();
 
     return {
-        addToCart, removeFromCart, selectRow,
+        addToCart, removeFromCart, clearCart, selectRow,
         updateQty, updateDiscount,
         addFromSearch, hideSearchResults,
         selectCustomer, clearCustomer,
@@ -1268,5 +1348,6 @@ const POS = (() => {
         connectThermal, thermalPrint,
         showOpenRegisterModal, closeOpenRegisterModal, openRegister,
         showCutZModal, closeCutZModal, loadCutX, confirmCutZ,
+        openCancelModal, closeCancelModal, changeQuantity, applyDiscount,
     };
 })();