fix: remove MapRazorComponents (use MapFallbackToFile only)

MapRazorComponents was causing 'Assembly already defined' error.
Fallback to MapFallbackToFile for static admin/index.html serving.

- Removed MapRazorComponents registration from Program.cs
- Keep MapFallbackToFile for SPA routing
- HTML with MudBlazor/admin.css loads correctly via fallback

Verified locally: HTTP 200, all assets present.

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

src/TaxBaik.Web/Program.cs

@@ -392,11 +392,6 @@ app.MapHealthChecks("/healthz");
 app.MapRazorPages();  // Sitemap.cshtml, Rss.cshtml, Feed.cshtml
 app.MapStaticAssets();
 
-// Blazor WebAssembly Admin Client
-app.MapRazorComponents<TaxBaik.WasmClient.Components.Admin.App>()
-   .AddInteractiveWebAssemblyRenderMode()
-   .AllowAnonymous();
-
 // SPA 라우팅 폴백 (가장 마지막에!)
 app.MapFallbackToFile("admin/{*path:nonfile}", "admin/index.html");