Add authentication support with login/logout UI

- Introduced AuthService, IAuthApiClient, and AuthApiClient for managing authentication state and API calls (login, logout, session restore).
- Added Login.razor and LoginLayout.razor for the login page, including styling and logic.
- MainLayout.razor now checks authentication on load, restores sessions from sessionStorage, and redirects to /login if unauthenticated. Displays username and logout button when logged in.
- Implemented JS interop (authStorage) for persisting authentication info in sessionStorage.
- Registered AuthService, CookieContainer, and API clients in Program.cs to share cookies and support authentication.
- Updated AppSettings and appsettings files to support separate ApiBaseUrl and DataApiBaseUrl.
- Minor CSS improvements for username display in the top bar.

DbFirst.BlazorWebApp/Components/Layout/MainLayout.razor

@@ -2,6 +2,9 @@
 @implements IDisposable
 @inject ThemeState ThemeState
 @inject IJSRuntime JS
+@inject AuthService AuthService
+@inject IAuthApiClient AuthApiClient
+@inject NavigationManager Navigation
 
 <div class="page @(ThemeState.IsDarkMode ? "app-dark" : "app-light") @(ThemeState.IsNativeDarkTheme ? "native-dark" : "")">
     <div class="sidebar">
@@ -18,11 +21,29 @@
                 <DxButton Text="@(ThemeState.IsDarkMode ? "Dark Mode aus" : "Dark Mode an")"
                           Click="ToggleTheme" />
             </span>
+            @if (AuthService.IsAuthenticated)
+            {
+                <span class="ms-auto d-flex align-items-center gap-2">
+                    <span class="top-row-username">@AuthService.UserName</span>
+                    <DxButton Text="Abmelden"
+                              Click="LogoutAsync"
+                              RenderStyle="ButtonRenderStyle.Secondary" />
+                </span>
+            }
             <a href="https://learn.microsoft.com/aspnet/core/" target="_blank">About</a>
         </div>
 
         <article class="content px-4">
-            @Body
+            @if (_checkingAuth)
+            {
+                <div class="loading-container">
+                    <span>Wird geladen…</span>
+                </div>
+            }
+            else
+            {
+                @Body
+            }
         </article>
     </main>
 </div>
@@ -35,10 +56,12 @@
 
 @code {
     private bool _isInteractive;
+    private bool _checkingAuth = true;
 
     protected override void OnInitialized()
     {
         ThemeState.OnChange += OnThemeChanged;
+        AuthService.OnChange += OnAuthChanged;
     }
 
     protected override async Task OnAfterRenderAsync(bool firstRender)
@@ -46,17 +69,71 @@
         if (firstRender)
         {
             _isInteractive = true;
+
+            if (!AuthService.IsAuthenticated)
+            {
+                try
+                {
+                    var username = await JS.InvokeAsync<string?>("authStorage.get", "auth_user");
+                    var cookie = await JS.InvokeAsync<string?>("authStorage.get", "auth_cookie");
+
+                    if (!string.IsNullOrEmpty(username) && !string.IsNullOrEmpty(cookie))
+                    {
+                        var restored = await AuthApiClient.RestoreAsync(username, cookie);
+                        if (!restored)
+                        {
+                            await JS.InvokeVoidAsync("authStorage.clear");
+                            Navigation.NavigateTo("/login", replace: true);
+                            return;
+                        }
+                    }
+                    else
+                    {
+                        Navigation.NavigateTo("/login", replace: true);
+                        return;
+                    }
+                }
+                catch
+                {
+                    Navigation.NavigateTo("/login", replace: true);
+                    return;
+                }
+            }
+
+            _checkingAuth = false;
+            StateHasChanged();
         }
+
         await ApplyDxDarkOverrideAsync();
     }
 
+    private async Task LogoutAsync()
+    {
+        try
+        {
+            await AuthApiClient.LogoutAsync();
+            await JS.InvokeVoidAsync("authStorage.clear");
+        }
+        catch
+        {
+            // Fehler beim Abmelden ignorieren, trotzdem weiterleiten
+        }
+
+        Navigation.NavigateTo("/login", replace: true);
+    }
+
+    private void OnAuthChanged()
+    {
+        InvokeAsync(StateHasChanged);
+    }
+
     private void OnThemeChanged()
     {
         InvokeAsync(async () =>
         {
             StateHasChanged();
             if (_isInteractive)
-             await ApplyDxDarkOverrideAsync();
+                await ApplyDxDarkOverrideAsync();
         });
     }
 
@@ -82,5 +159,6 @@
     public void Dispose()
     {
         ThemeState.OnChange -= OnThemeChanged;
+        AuthService.OnChange -= OnAuthChanged;
     }
 }