feat(pos/workshop): add 80mm thermal ticket printing for service orders

- Add generate_service_order_ticket() in thermal_printer.py with ESC/POS commands for 58mm and 80mm printers.

- Add POST /pos/api/service-orders/:id/print endpoint returning raw bytes or JSON for browser rendering.

- Extend printer.js with printServiceOrder() using WebUSB/Web Serial.

- Add Imprimir orden button in workshop.js detail modal.

- Update FASES_IMPLEMENTADAS.md.

pos/static/js/workshop.js

@@ -250,6 +250,7 @@ var Workshop = (function() {
         var footer = document.getElementById('detailFooter');
         footer.innerHTML =
             '<button class="btn btn--ghost" onclick="Workshop.closeDetailModal()">Cerrar</button>' +
+            '<button class="btn btn--secondary" onclick="Workshop.printOrder()">🖨️ Imprimir orden</button>' +
             (o.status === 'ready' && !o.sale_id ? '<button class="btn btn--primary" onclick="Workshop.convertToSale()">Convertir a venta</button>' : '') +
             (o.sale_id ? '<a class="btn btn--secondary" href="/pos/invoicing?sale_id=' + o.sale_id + '">Ver venta #' + o.sale_id + '</a>' : '');
     }
@@ -328,6 +329,29 @@ var Workshop = (function() {
         }).catch(function(e) { alert('Error: ' + e.message); });
     }
 
+    function printOrder() {
+        if (!currentOrderId) return;
+        if (!window.NexusPrinter || !window.NexusPrinter.isConnected()) {
+            var connect = confirm('No hay impresora conectada. ¿Conectar ahora?');
+            if (connect) {
+                window.NexusPrinter.connect().then(function(r) {
+                    if (r.ok) doPrint();
+                });
+            }
+            return;
+        }
+        doPrint();
+
+        function doPrint() {
+            window.NexusPrinter.printServiceOrder(currentOrderId, 80)
+                .then(function(ok) {
+                    if (ok) alert('Orden enviada a la impresora');
+                    else alert('No se pudo imprimir');
+                })
+                .catch(function(e) { alert('Error: ' + e.message); });
+        }
+    }
+
     // ─── New order ───
 
     function openNewOrderModal() {
@@ -469,6 +493,7 @@ var Workshop = (function() {
         addItemPlaceholder: addItemPlaceholder,
         addLabor: addLabor,
         convertToSale: convertToSale,
+        printOrder: printOrder,
         openNewOrderModal: openNewOrderModal,
         closeNewOrderModal: closeNewOrderModal,
         submitNewOrder: submitNewOrder,