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/accounting_bp.py

@@ -741,3 +741,45 @@ def close_period():
         cur.close()
         conn.close()
         return jsonify({'error': str(e)}), 500
+
+
+@accounting_bp.route('/stats', methods=['GET'])
+@require_auth('accounting.read')
+def api_accounting_stats():
+    """Return counts for tab badges: receivables (asset accounts with balance) and payables (liability accounts with balance)."""
+    conn = get_tenant_conn(g.tenant_id)
+    cur = conn.cursor()
+
+    # Count asset accounts with positive balance (cuentas por cobrar)
+    cur.execute("""
+        SELECT COUNT(*) FROM (
+            SELECT a.id
+            FROM accounts a
+            LEFT JOIN journal_entry_lines l ON l.account_id = a.id
+            WHERE a.type = 'activo' AND a.is_active = true
+            GROUP BY a.id
+            HAVING COALESCE(SUM(l.debit), 0) - COALESCE(SUM(l.credit), 0) > 0
+        ) x
+    """)
+    cxc = cur.fetchone()[0] or 0
+
+    # Count liability accounts with positive balance (cuentas por pagar)
+    cur.execute("""
+        SELECT COUNT(*) FROM (
+            SELECT a.id
+            FROM accounts a
+            LEFT JOIN journal_entry_lines l ON l.account_id = a.id
+            WHERE a.type = 'pasivo' AND a.is_active = true
+            GROUP BY a.id
+            HAVING COALESCE(SUM(l.credit), 0) - COALESCE(SUM(l.debit), 0) > 0
+        ) x
+    """)
+    cxp = cur.fetchone()[0] or 0
+
+    cur.close()
+    conn.close()
+
+    return jsonify({
+        'cuentas_cobrar': cxc,
+        'cuentas_pagar': cxp,
+    })