Add remember username on login

src/dotnet/QuantEngine.Web/Client/Pages/Login.razor

@@ -18,6 +18,7 @@
         <MudStack Spacing="2">
             <MudTextField Label="관리자 아이디" @bind-Value="Username" Variant="Variant.Outlined" Immediate="true" AutoFocus="true" />
             <MudTextField Label="비밀번호" @bind-Value="Password" Variant="Variant.Outlined" InputType="InputType.Password" Immediate="true" />
+            <MudCheckBox T="bool" @bind-Checked="RememberUsername" Color="Color.Primary" Label="아이디 저장" />
 
             @if (!string.IsNullOrEmpty(ErrorMessage))
             {
@@ -57,6 +58,18 @@
     private string Password { get; set; } = string.Empty;
     private string ErrorMessage { get; set; } = string.Empty;
     private bool IsSubmitting { get; set; } = false;
+    private bool RememberUsername { get; set; } = true;
+
+    protected override async Task OnInitializedAsync()
+    {
+        var customProvider = (CustomAuthenticationStateProvider)AuthStateProvider;
+        var remembered = await customProvider.GetRememberedUsernameAsync();
+        if (!string.IsNullOrWhiteSpace(remembered))
+        {
+            Username = remembered;
+            RememberUsername = true;
+        }
+    }
 
     private sealed class LoginResponse
     {
@@ -91,7 +104,7 @@
                 }
 
                 var customProvider = (CustomAuthenticationStateProvider)AuthStateProvider;
-                await customProvider.MarkUserAsAuthenticatedAsync(auth.Username ?? Username, auth.AccessToken, auth.Role ?? "Admin");
+                await customProvider.MarkUserAsAuthenticatedAsync(auth.Username ?? Username, auth.AccessToken, auth.Role ?? "Admin", RememberUsername);
                 NavigationManager.NavigateTo("/dashboard");
             }
             else