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_set_password.dart

@@ -26,10 +26,10 @@ class DesktopSetPasswordState extends State<DesktopSetPassword> {
   final passwordController = TextEditingController();
   final passwordAgainController = TextEditingController();
 
-  bool passwordVisible;
-  bool passwordAgainVisible;
+  late bool passwordVisible;
+  late bool passwordAgainVisible;
 
-  bool canReset;
+  late bool canReset;
 
   double sideSpace = 0;
   double mainSpace = 1200;
@@ -93,7 +93,7 @@ class DesktopSetPasswordState extends State<DesktopSetPassword> {
                     fontSize: 18.0
                 ),
                 validator: (String? value) {
-                  if (value.trim().isEmpty) {
+                  if (value!.trim().isEmpty) {
                     return S.of(context).password_is_required;
                   }
                   return null;
@@ -147,10 +147,10 @@ class DesktopSetPasswordState extends State<DesktopSetPassword> {
                     fontSize: 18.0
                 ),
                 validator: (String? value) {
-                  if (value.trim().isEmpty) {
+                  if (value!.trim().isEmpty) {
                     return S.of(context).password_is_required;
                   }
-                  if (value.trim() != passwordController.text.trim()) {
+                  if (value!.trim() != passwordController.text.trim()) {
                     return S.of(context).password_is_not_match_password_again;
                   }
                   return null;