feat(auth): add sendCodeSilently with isSending state

apps/lib/features/auth/presentation/cubits/register_cubit.dart

@@ -16,6 +16,7 @@ class RegisterState extends Equatable {
   final String? errorMessage;
   final String? pendingEmail;
   final bool codeSent;
+  final bool isSending;
 
   const RegisterState({
     this.username = const Username.pure(),
@@ -26,6 +27,7 @@ class RegisterState extends Equatable {
     this.errorMessage,
     this.pendingEmail,
     this.codeSent = false,
+    this.isSending = false,
   });
 
   bool get isStep1Valid =>
@@ -41,6 +43,7 @@ class RegisterState extends Equatable {
     String? errorMessage,
     String? pendingEmail,
     bool? codeSent,
+    bool? isSending,
   }) {
     return RegisterState(
       username: username ?? this.username,
@@ -51,6 +54,7 @@ class RegisterState extends Equatable {
       errorMessage: errorMessage,
       pendingEmail: pendingEmail ?? this.pendingEmail,
       codeSent: codeSent ?? this.codeSent,
+      isSending: isSending ?? this.isSending,
     );
   }
 
@@ -64,6 +68,7 @@ class RegisterState extends Equatable {
     errorMessage,
     pendingEmail,
     codeSent,
+    isSending,
   ];
 }
 
@@ -160,4 +165,31 @@ class RegisterCubit extends Cubit<RegisterState> {
       emit(state.copyWith(errorMessage: message));
     }
   }
+
+  Future<void> sendCodeSilently() async {
+    if (!state.isStep1Valid) return;
+
+    emit(state.copyWith(isSending: true));
+
+    try {
+      final response = await _repository.signupStart(
+        SignupStartRequest(
+          username: state.username.value,
+          email: state.email.value,
+          password: state.password.value,
+        ),
+      );
+      emit(
+        state.copyWith(
+          isSending: false,
+          pendingEmail: response.email,
+          codeSent: true,
+          errorMessage: null,
+        ),
+      );
+    } catch (e) {
+      final message = e is ApiException ? e.message : '验证码发送失败，请重试';
+      emit(state.copyWith(isSending: false, errorMessage: message));
+    }
+  }
 }