phase3: nullfix.py batch script — bang/late/param-nullable

Automated null-safety fixes driven by dart analyze (no corruption):
- unchecked_use_of_nullable_value: insert '!' on receiver (property/method/[]/op)
- not_initialized field/var: mark 'late'
- missing_default_value_for_parameter: nullable param
Errors: 2374(peak) -> 907

lib/widgets/desktop/desktop_edit_address.dart

@@ -45,12 +45,12 @@ class DesktopEditAddressState extends State<DesktopEditAddress> {
   final emailController = TextEditingController();
   final faxController = TextEditingController();
 
-  String country;
-  Gender _selectedGender;
+  late String country;
+  late Gender _selectedGender;
 
-  String _selectedProvince;
+  late String _selectedProvince;
 
-  bool showLoading;
+  late bool showLoading;
 
   double sideSpace = 0;
   double mainSpace = 1200;
@@ -362,7 +362,7 @@ class DesktopEditAddressState extends State<DesktopEditAddress> {
                     .email,
               ),
               validator: (String? value) {
-                if (value.isNotEmpty && !EmailValidator.validate(value)) {
+                if (value!.isNotEmpty && !EmailValidator.validate(value)) {
                   return S
                       .of(context)
                       .email_is_not_valid;