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/mobile/mobile_new_user.dart

@@ -28,9 +28,9 @@ class MobileNewUserState extends State<MobileNewUser> {
   bool usernameEnable = true;
   final codeController = TextEditingController();
 
-  bool enableGetCode;
-  String getCodeText;
-  bool canRegister;
+  late bool enableGetCode;
+  late String getCodeText;
+  late bool canRegister;
 
   var countDownListener;
 
@@ -88,7 +88,7 @@ class MobileNewUserState extends State<MobileNewUser> {
                     ),
                     autofocus: true,
                     validator: (String? value) {
-                      if (value.trim().isEmpty) {
+                      if (value!.trim().isEmpty) {
                         return S.of(context).mobile_or_email_is_required;
                       }
                       return null;
@@ -171,7 +171,7 @@ class MobileNewUserState extends State<MobileNewUser> {
                         fontSize: 18.0
                     ),
                     validator: (String? value) {
-                      if (value.trim().isEmpty) {
+                      if (value!.trim().isEmpty) {
                         return S.of(context).verification_code_is_required;
                       }
                       return null;