feat: create Blazor-based login component with EmptyLayout

- Create Login.razor component at /login path with Blazor form
- Create EmptyLayout to prevent MainLayout wrapping on login page
- Update Program.cs to redirect unauthenticated users to /login (Blazor route)
- Integrate with CustomAuthenticationStateProvider for proper auth state management
- Handle authentication response and token storage

Note: Login flow still has routing issues - investigating dashboard redirect

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

src/dotnet/QuantEngine.Web/Program.cs

@@ -178,13 +178,13 @@ catch (Exception ex)
     Log.Warning("Hangfire setup failed: {Message}", ex.Message);
 }
 
-// Root path - redirect unauthenticated to login.html
+// Root path - redirect unauthenticated to /login (Blazor component)
 app.MapGet("/", async (HttpContext ctx) =>
 {
     var isAuthenticated = ctx.User?.Identity?.IsAuthenticated ?? false;
     if (!isAuthenticated)
     {
-        ctx.Response.Redirect("/login.html");
+        ctx.Response.Redirect("/login");
     }
     else
     {
@@ -194,12 +194,6 @@ app.MapGet("/", async (HttpContext ctx) =>
     await Task.CompletedTask;
 });
 
-// Redirect /login to /login.html (static file)
-app.MapGet("/login", (HttpContext ctx) =>
-{
-    ctx.Response.Redirect("/login.html", permanent: false);
-});
-
 // Collection API Endpoints (must be before MapRazorComponents)
 app.MapCollectionEndpoints();