Enhance external login and proxy compatibility

- Updated `ExternalLoginPicker.razor` to add Google and Microsoft login buttons with SVG icons and improved styling.
- Added new styles in `ExternalLoginPicker.razor.css` for layout and accessibility.
- Configured `ForwardedHeadersOptions` and enabled `UseForwardedHeaders` middleware in `Program.cs` for reverse proxy support.
- Added `AddCascadingAuthenticationState` for better authentication state management.
- Included `microsoft-identity-association.json` for Microsoft app association.
- Added `google-signin.svg` and `microsoft-signin.svg` assets for login buttons.

src/BirthList.Web/Program.cs

@@ -4,6 +4,7 @@ using BirthList.Web.Configuration;
 using BirthList.Web.Features.Registries;
 using BirthList.Web.Services;
 using Microsoft.AspNetCore.Components.Authorization;
+using Microsoft.AspNetCore.HttpOverrides;
 using Microsoft.AspNetCore.Identity;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Infrastructure;
@@ -25,6 +26,13 @@ builder.Services.AddHttpClient("RegistryMetadata", client =>
 });
 builder.Services.Configure<SmtpOptions>(builder.Configuration.GetSection("Smtp"));
 
+builder.Services.Configure<ForwardedHeadersOptions>(options =>
+{
+    options.ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto;
+    options.KnownNetworks.Clear();
+    options.KnownProxies.Clear();
+});
+
 builder.Services.AddCascadingAuthenticationState();
 builder.Services.AddScoped<IdentityUserAccessor>();
 builder.Services.AddScoped<IdentityRedirectManager>();
@@ -150,6 +158,7 @@ else
     app.UseHsts();
 }
 
+app.UseForwardedHeaders();
 app.UseHttpsRedirection();
 
 app.UseStaticFiles();