fix: disable prerender for login page to enable Blazor event handlers

Problem: Login.razor with prerender: true converts Blazor MudForm's @OnSubmit
directive to static HTML form submit, which doesn't call HandleLogin C# method.
Result: 'HandleLogin is not defined' ReferenceError.

Solution: Set prerender: false for login page. WASM boots before rendering,
so Blazor event handlers work correctly. Minor UX trade-off (brief spinner while
WASM loads) is acceptable for full functionality.

Result: Login form now properly invokes HandleLogin, updates authentication state,
and navigates to dashboard.

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

src/TaxBaik.Web.Client/Components/Admin/Pages/Login.razor

@@ -1,6 +1,6 @@
 @page "/admin/login"
 @layout TaxBaik.WasmClient.Components.Admin.Layout.BlankLayout
 @attribute [AllowAnonymous]
-@rendermode @(new InteractiveWebAssemblyRenderMode(prerender: true))
+@rendermode @(new InteractiveWebAssemblyRenderMode(prerender: false))
 <PageTitle>로그인</PageTitle>
 <AdminLoginForm />