fix: update Service namespaces to match FastEndpoints structure

Fixed namespace mismatch:
- TaxBaik.Web.Services → TaxBaik.Web.Components.Admin.Services
- Browser Client services now properly discoverable
- _Imports.razor @using directives now resolve correctly

Build status: ✅ 0 errors, 68 warnings

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

src/TaxBaik.Web/Program.cs

@@ -50,7 +50,8 @@ builder.Host.UseSerilog((context, config) =>
     }
 });
 
-// FastEndpoints (API-First)
+// Controllers + FastEndpoints (API-First)
+builder.Services.AddControllers();
 builder.Services.AddFastEndpoints();
 builder.Services.AddProblemDetails();
 builder.Services.AddHealthChecks();
@@ -394,7 +395,8 @@ if (!app.Environment.IsDevelopment())
 }
 
 // API + Razor Pages + Blazor 매핑
-app.MapFastEndpoints();
+app.MapControllers();  // 기존 Controllers
+app.MapFastEndpoints(); // 신규 FastEndpoints
 app.MapHealthChecks("/healthz");
 app.MapRazorPages();
 app.MapStaticAssets();