fix: consolidate backend changes and fix icon imports

- Add standard .gitignore patterns (node_modules, .env, IDE files)
- Coupon.php: fix data structure for DataTable, add status filter
- Order.php: fix data structure to match OrderListItem expectations
- Product.php: add multi-currency prices array, unify nonce to 'formipay-admin'
- client.js: fix AJAX action names to match PHP (underscores → hyphens)
- OrderList.js: fix icon import (Icons.list), add response handling
- OrderListItem.js: fix icon import (Icons.seen)

.gitignore

@@ -1 +1,12 @@
-.DS_Store
+.DS_Store
+node_modules
+coverage
+.env
+*.log
+.idea
+.vscode
+*.suo
+*.ntvs*
+*.njsproj
+*.sln
+*.sw?