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/Client/Layout/EmptyLayout.razor

@@ -0,0 +1,16 @@
+@inherits LayoutComponentBase
+
+@Body
+
+<style>
+    :global(html, body) {
+        height: 100%;
+        margin: 0;
+        padding: 0;
+    }
+
+    :global(#app) {
+        display: flex;
+        min-height: 100vh;
+    }
+</style>