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/blueprints/marketplace_bp.py

@@ -190,6 +190,16 @@ def bodegas_with_part(part_id):
     return _with_master(_do)
 
 
+@marketplace_bp.route('/inventory/listing/<int:wi_id>', methods=['GET'])
+@require_auth()
+def bodegas_with_listing(wi_id):
+    """Return bodegas stocking a specific seller listing (wi_id)."""
+    def _do(master):
+        data = mkt.get_bodegas_with_listing(master, wi_id)
+        return jsonify({'data': data, 'count': len(data)})
+    return _with_master(_do)
+
+
 # ═══════════════════════════════════════════════════════════════════════════
 # PURCHASE ORDERS
 # ═══════════════════════════════════════════════════════════════════════════