feat: Migrate label printing module from legacy app

- Created labels module with complete structure in app/modules/labels/
- Implemented print_module.py with database functions:
  * get_unprinted_orders_data() - Retrieve unprinted orders from database
  * get_printed_orders_data() - Retrieve printed orders from database
  * update_order_printed_status() - Mark orders as printed
  * search_orders_by_cp_code() - Search orders by production code
- Created routes.py with Flask Blueprint and API endpoints:
  * GET /labels/ - Module home page with feature launchers
  * GET /labels/print-module - Main label printing interface
  * GET /labels/print-lost-labels - Lost label reprinting interface
  * GET /labels/api/unprinted-orders - API for unprinted orders
  * GET /labels/api/printed-orders - API for printed orders
  * POST /labels/api/search-orders - Search orders API
  * POST /labels/api/update-printed-status/<id> - Update status API
- Migrated HTML templates from legacy app with theme support:
  * print_module.html - Thermal label printing with QZ Tray integration
  * print_lost_labels.html - Lost label search and reprint interface
  * Added comprehensive CSS variables for dark/light mode theming
  * Preserved all original JavaScript functionality for printing
- Created index.html module home page with feature launchers
- Registered labels blueprint in app/__init__.py with /labels prefix
- Added 'Label Printing' module card to dashboard with print icon

All functionality preserved from original implementation:
- QZ Tray thermal printer integration
- JsBarcode barcode generation (horizontal + vertical)
- PDF export fallback
- Session-based authentication for all routes
- Database integration with proper error handling

app/routes.py

@@ -86,6 +86,13 @@ def dashboard():
             'color': 'info',
             'url': url_for('warehouse.warehouse_index')
         },
+        {
+            'name': 'Label Printing',
+            'description': 'Print and manage thermal labels for orders',
+            'icon': 'fa-print',
+            'color': 'success',
+            'url': url_for('labels.labels_index')
+        },
         {
             'name': 'Settings',
             'description': 'Configure application settings',