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/catalog.js

@@ -349,10 +349,14 @@
         var cacheKey = 'nexus:brands:' + catalogMode;
         var cached = sessionStorage.getItem(cacheKey);
         if (cached) {
-            hideLoading();
-            var data = JSON.parse(cached);
-            renderBrands(data);
-            return;
+            try {
+                hideLoading();
+                var data = JSON.parse(cached);
+                renderBrands(data);
+                return;
+            } catch (e) {
+                sessionStorage.removeItem(cacheKey);
+            }
         }
 
         apiFetch(API + '/brands?mode=' + catalogMode).then(function (data) {
@@ -1631,8 +1635,13 @@
         var cacheKey = 'nexus:years-all';
         var cached = sessionStorage.getItem(cacheKey);
         if (cached) {
-            var data = JSON.parse(cached);
-            var years = data.data || data || [];
+            try {
+                var data = JSON.parse(cached);
+                var years = data.data || data || [];
+            } catch (e) {
+                sessionStorage.removeItem(cacheKey);
+                var years = [];
+            }
             if (!years.length) {
                 years = [];
                 for (var y = 2026; y >= 1990; y--) years.push({ id_year: y, year_car: y });