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.)

pubspec.yaml

@@ -18,7 +18,8 @@ publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 version: 1.0.1+2
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: ">=3.0.0 <4.0.0"
+  flutter: ">=3.29.0"
 
 dependencies:
   flutter:
@@ -77,13 +78,7 @@ dependencies:
   toggle_switch: ^1.2.0
   pinput: ^1.2.0
   google_maps_flutter: ^2.0.6 #^1.2.0
-  stripe_payment: ^1.0.10
-#  stripe_sdk:
-#    git:
-#      url: git://github.com/romme86/stripe-sdk.git
-  stripe_sdk:
-    git:
-      url: https://github.com/ezet/stripe-sdk.git
+# Stripe removed — switched to e-Transfer. See UPGRADE_NOTES.md.
   uuid: ^3.0.4 #^2.2.2
   ffi: ^1.0.0
 #  firebase_messaging: ^10.0.4 #^7.0.3