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_user_profile.dart

@@ -27,10 +27,10 @@ class DesktopUserProfile extends StatefulWidget {
 }
 
 class DesktopUserProfileState extends State<DesktopUserProfile> {
-  User _user;
+  late User _user;
 
-  bool _showProgress;
-  double _progress;
+  late bool _showProgress;
+  late double _progress;
 
   double sideSpace = 0;
   double mainSpace = 1200;
@@ -253,7 +253,7 @@ class DesktopUserProfileState extends State<DesktopUserProfile> {
                         ),
                         Container(
                           child: Text(
-                            _user.mobile != null && _user.mobile.isNotEmpty ? Utils.safePhoneNumber(_user.mobile) : S.of(context).not_binding,
+                            _user.mobile != null && _user.mobile!.isNotEmpty ? Utils.safePhoneNumber(_user.mobile) : S.of(context).not_binding,
                             style: TextStyle(
                               color: Colors.grey,
                             ),
@@ -306,7 +306,7 @@ class DesktopUserProfileState extends State<DesktopUserProfile> {
                         ),
                         Container(
                           child: Text(
-                            _user.email != null && _user.email.isNotEmpty ? Utils.safePhoneNumber(_user.email) : S.of(context).not_binding,
+                            _user.email != null && _user.email!.isNotEmpty ? Utils.safePhoneNumber(_user.email) : S.of(context).not_binding,
                             style: TextStyle(
                               color: Colors.grey,
                             ),
@@ -425,7 +425,7 @@ class DesktopUserProfileState extends State<DesktopUserProfile> {
                   ),
                   autofocus: true,
                   validator: (String? value) {
-                    if (value.trim().isEmpty) {
+                    if (value!.trim().isEmpty) {
                       return S.of(context).nickname_is_required;
                     }
                     return null;