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/whatsapp2.js

@@ -16,6 +16,7 @@
   var activePhone = null;
   var pollTimer = null;
   var statusPollTimer = null;
+  var qrPollTimer = null;
   var connectionState = 'unknown'; // 'open', 'close', 'connecting', 'unknown'
 
   // -- Helpers ---------------------------------------------------------------
@@ -88,6 +89,10 @@
     api('GET', '/status').then(function (data) {
       var state = (data.instance || data).state || data.state || 'close';
       updateConnectionUI(state);
+      // If bridge already has a QR ready, show it immediately
+      if (state === 'qr' || state === 'connecting') {
+        fetchQR();
+      }
     }).catch(function () {
       updateConnectionUI('close');
     });
@@ -106,7 +111,8 @@
       // Load conversations + start polling on page load / reconnect
       loadConversations();
       startPolling();
-    } else if (state === 'connecting') {
+      stopQRPolling();
+    } else if (state === 'connecting' || state === 'qr') {
       statusDot.className = 'status-dot status-dot--warn';
       statusText.textContent = 'Escaneando QR...';
       connectSection.style.display = 'flex';
@@ -125,6 +131,7 @@
       refreshQrBtn.style.display = 'none';
       qrImg.style.display = 'none';
       qrPlaceholder.style.display = '';
+      stopQRPolling();
     }
   }
 
@@ -141,8 +148,15 @@
         return;
       }
 
-      // Instance created, now fetch QR
-      fetchQR();
+      // Switch UI to connecting state immediately
+      updateConnectionUI('connecting');
+      qrPlaceholder.textContent = 'Iniciando conexion con WhatsApp, generando QR...';
+      qrPlaceholder.style.display = '';
+      qrImg.style.display = 'none';
+
+      // Start polling for QR; the first fetchQR may not have QR ready yet
+      startStatusPolling();
+      startQRPolling();
     }).catch(function () {
       connectBtn.disabled = false;
       connectBtn.textContent = 'Conectar WhatsApp';
@@ -151,7 +165,10 @@
   }
 
   function fetchQR() {
-    qrPlaceholder.textContent = 'Generando QR...';
+    // Only update placeholder text if we don't already have a QR image showing
+    if (qrImg.style.display !== 'block') {
+      qrPlaceholder.textContent = 'Generando codigo QR, espera unos segundos...';
+    }
 
     api('GET', '/qr').then(function (data) {
       var base64 = data.qr || data.base64 || data.qrcode || '';
@@ -164,14 +181,18 @@
 
         // Start polling for connection state while QR is shown
         startStatusPolling();
+        startQRPolling();
       } else if ((data.instance && data.instance.state === 'open') || data.state === 'open') {
         // Already connected
         updateConnectionUI('open');
         loadConversations();
       } else {
-        qrPlaceholder.textContent = 'No se pudo generar el QR. Intenta de nuevo.';
-        qrPlaceholder.style.display = '';
-        qrImg.style.display = 'none';
+        // QR not ready yet — this is normal right after pressing Connect
+        if (qrImg.style.display !== 'block') {
+          qrPlaceholder.textContent = 'Generando codigo QR, por favor espera... (el codigo cambia cada pocos segundos, escanealo en cuanto aparezca)';
+          qrPlaceholder.style.display = '';
+          qrImg.style.display = 'none';
+        }
       }
     }).catch(function () {
       qrPlaceholder.textContent = 'Error al obtener QR';
@@ -208,6 +229,24 @@
     }
   }
 
+  function startQRPolling() {
+    stopQRPolling();
+    qrPollTimer = setInterval(function () {
+      if (connectionState === 'connecting' || connectionState === 'qr') {
+        fetchQR();
+      } else {
+        stopQRPolling();
+      }
+    }, 5000);
+  }
+
+  function stopQRPolling() {
+    if (qrPollTimer) {
+      clearInterval(qrPollTimer);
+      qrPollTimer = null;
+    }
+  }
+
   connectBtn.addEventListener('click', doConnect);
   disconnectBtn.addEventListener('click', doDisconnect);
   refreshQrBtn.addEventListener('click', fetchQR);