feat: Phase 1 — remove Stripe, switch to e-Transfer

- Drop stripe_payment + stripe_sdk deps; delete stripe pay pages/widgets
- New ETransferPay widget: shows payment@wisetronic.com + R#<orderId> remark
- goPayment stripe/native branches now route to e-Transfer
- pay_now widgets: strip saved-cards section & dead nativePay logic
- my_cards pages rewritten as e-Transfer info (route kept)
- models/utils/constants cleaned of stripe; env constraint -> Dart 3

See UPGRADE_NOTES.md. (Null-safety migration is Phase 3; deps upgrade Phase 2.)

lib/models/user.dart

@@ -1,8 +1,6 @@
 
 import 'dart:convert';
 
-import 'stripe_payment_method.dart';
-
 class User {
   int id;
   String username;
@@ -20,7 +18,6 @@ class User {
   double pointsToCreditsConversionRate;
   String contactNumber;
   String flutterMiniStoreToken;
-  List<StripePaymentMethod> stripePaymentMethods;
 
   User.fromJson(Map<String, dynamic> json)
       : id = json['id'],
@@ -38,8 +35,7 @@ class User {
         orderNum = json['order_num'],
         pointsToCreditsConversionRate = double.parse(json['points_to_credits_conversion_rate'].toString()),
         contactNumber = json['contact_number'],
-        flutterMiniStoreToken = json['flutter_ministore_token'],
-        stripePaymentMethods = (json['stripe_payment_methods'] as List).map((e) => StripePaymentMethod.fromJson(e)).toList();
+        flutterMiniStoreToken = json['flutter_ministore_token'];
 
   Map<String, dynamic> toJson() => {
     'id': id,
@@ -58,7 +54,6 @@ class User {
     'points_to_credits_conversion_rate': pointsToCreditsConversionRate,
     'contact_number': contactNumber,
     'flutter_ministore_token': flutterMiniStoreToken,
-    'stripe_payment_methods': stripePaymentMethods,
   };
 
   @override