Fix QZ Tray library loading and add pairing keys API endpoint

- Fix QZ Tray library loading errors (net::ERR_NAME_NOT_RESOLVED) by switching from CDN to local static file
- Add /labels/api/pairing-keys endpoint to fetch valid printer pairing keys
- Update print_labels.html to use local js/qz-tray.js
- Update print_lost_labels.html to use local js/qz-tray.js
- Update print_lost_labels_new.html to use correct path js/qz-tray.js
- Update fg_scan.html to use local js/qz-tray.js
- API returns active pairing keys from qz_pairing_keys table for printer selection

app/modules/labels/routes.py

@@ -487,4 +487,39 @@ def api_generate_batch_pdf(order_id):
         
     except Exception as e:
         logger.error(f"Error generating batch PDF: {e}")
+        return jsonify({'error': str(e)}), 500
+
+
+@labels_bp.route('/api/pairing-keys', methods=['GET'], endpoint='api_pairing_keys')
+def api_pairing_keys():
+    """Get QZ Tray pairing keys for printer selection"""
+    if 'user_id' not in session:
+        return jsonify({'error': 'Unauthorized'}), 401
+    
+    try:
+        conn = get_db()
+        cursor = conn.cursor()
+        
+        cursor.execute("""
+            SELECT id, printer_name, pairing_key, valid_until 
+            FROM qz_pairing_keys 
+            WHERE valid_until >= CURDATE()
+            ORDER BY printer_name ASC
+        """)
+        
+        pairing_keys = []
+        for row in cursor.fetchall():
+            pairing_keys.append({
+                'id': row[0],
+                'printer_name': row[1],
+                'pairing_key': row[2]
+            })
+        
+        cursor.close()
+        
+        logger.info(f"Retrieved {len(pairing_keys)} valid pairing keys")
+        return jsonify(pairing_keys), 200
+        
+    except Exception as e:
+        logger.error(f"Error fetching pairing keys: {e}")
         return jsonify({'error': str(e)}), 500

app/templates/modules/labels/print_labels.html

@@ -290,8 +290,11 @@
 <!-- Add html2canvas library for capturing preview as image -->
 <script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/1.4.1/html2canvas.min.js"></script>
 <!-- PATCHED QZ Tray library - works with custom server using pairing key authentication -->
+<script src="{{ url_for('static', filename='js/qz-tray.js') }}"></script>
+<!-- CDN versions (disabled): 
 <script src="https://qz.glyphtree.com/api/latest/qz-tray.js"></script>
-<!-- Original CDN version (disabled): <script src="https://cdn.jsdelivr.net/npm/qz-tray@2.2.4/qz-tray.js"></script> -->
+<script src="https://cdn.jsdelivr.net/npm/qz-tray@2.2.4/qz-tray.js"></script> 
+-->
 
 <script>
 // Simplified notification system

app/templates/modules/labels/print_lost_labels.html

@@ -237,7 +237,7 @@
 <!-- Add html2canvas library for capturing preview as image -->
 <script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/1.4.1/html2canvas.min.js"></script>
 <!-- PATCHED QZ Tray library - works with custom server using pairing key authentication -->
-<script src="https://qz.glyphtree.com/api/latest/qz-tray.js"></script>
+<script src="{{ url_for('static', filename='js/qz-tray.js') }}"></script>
 <script>
 
 // Store all orders data for searching (will be populated by API fetch on page load)

app/templates/modules/labels/print_lost_labels_new.html

@@ -230,7 +230,7 @@
 <!-- Add html2canvas library for capturing preview as image -->
 <script src="{{ url_for('static', filename='html2canvas.min.js') }}"></script>
 <!-- PATCHED QZ Tray library - works with custom server using pairing key authentication -->
-<script src="{{ url_for('static', filename='qz-tray.js') }}"></script>
+<script src="{{ url_for('static', filename='js/qz-tray.js') }}"></script>
 <script>
 
 // Store all orders data for searching

app/templates/modules/quality/fg_scan.html

@@ -4,7 +4,7 @@
 
 {% block extra_css %}
 <link rel="stylesheet" href="{{ url_for('static', filename='css/fg_scan.css') }}">
-<script src="https://cdn.jsdelivr.net/npm/qz-tray@2.1.0/qz-tray.js"></script>
+<script src="{{ url_for('static', filename='js/qz-tray.js') }}"></script>
 {% endblock %}
 
 {% block content %}