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/printer.js

@@ -134,6 +134,31 @@ window.NexusPrinter = (function () {
         return sendRaw(new Uint8Array(buf));
     }
 
+    /**
+     * Print a workshop service order ticket.
+     * @param {number} soId
+     * @param {number} [width=80] — 58 or 80 mm
+     * @returns {Promise<boolean>}
+     */
+    async function printServiceOrder(soId, width) {
+        width = width || 80;
+        const token = localStorage.getItem('pos_token');
+        const resp = await fetch('/pos/api/service-orders/' + soId + '/print', {
+            method: 'POST',
+            headers: {
+                'Authorization': 'Bearer ' + token,
+                'Content-Type': 'application/json'
+            },
+            body: JSON.stringify({ printer_type: 'escpos_raw', width: width })
+        });
+        if (!resp.ok) {
+            console.error('[NexusPrinter] backend error', resp.status);
+            return false;
+        }
+        const buf = await resp.arrayBuffer();
+        return sendRaw(new Uint8Array(buf));
+    }
+
     // ── Persistence helpers ────────────────────────
 
     function _save() {
@@ -147,6 +172,7 @@ window.NexusPrinter = (function () {
         disconnect: disconnect,
         isConnected: isConnected,
         sendRaw: sendRaw,
-        printSale: printSale
+        printSale: printSale,
+        printServiceOrder: printServiceOrder
     };
 })();