feat(auth): implement option 3 architecture - server InteractiveServer login + client WASM dashboard

- Add Server.AddInteractiveServerComponents() + AddInteractiveServerRenderMode()
- Create Server AuthLayout for login form (MudBlazor)
- Implement LoginSimple.razor with @rendermode InteractiveServer in Server project
- Update App.razor: CascadingAuthenticationState + Router with AppAssembly=Server
- Fix Client MudBlazor Providers in MainLayout + AuthLayout
- Update Playwright tests: use dynamic selectors for MudTextField (auto-generated IDs)
- Build: 0 errors, 0 warnings
- API: /api/auth/login fully operational (200 OK confirmed)
- Playwright E2E test: 1 passed

Architecture:
/login    → Server InteractiveServer (MudBlazor form)
/         → Client WebAssembly (Dashboard)
/api/*    → Server Endpoints

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/dotnet/QuantEngine.Web/Client/Program.cs

@@ -2,6 +2,7 @@ using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
 using Microsoft.AspNetCore.Components.Authorization;
 using QuantEngine.Web.Client.Services;
 using QuantEngine.Web.Client.Infrastructure;
+using MudBlazor.Services;
 
 var builder = WebAssemblyHostBuilder.CreateDefault(args);
 
@@ -16,6 +17,9 @@ builder.Services.AddAuthorizationCore();
 builder.Services.AddCascadingAuthenticationState();
 builder.Services.AddScoped<AuthenticationStateProvider, CustomAuthenticationStateProvider>();
 
+// MudBlazor Services (CRITICAL: Required for Interactive WebAssembly)
+builder.Services.AddMudServices();
+
 // HttpClient register (API-First standard)
 builder.Services.AddScoped(sp => new HttpClient { BaseAddress = new Uri(builder.HostEnvironment.BaseAddress) });