Initial project setup: solution + 5 projects

- Domain, Infrastructure, Application (class libraries)
- Web (ASP.NET Core empty)
- Admin (Blazor Server)
- All net8.0 target framework
- Project references configured

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

TaxBaik.Admin/Pages/Error.cshtml.cs

@@ -0,0 +1,26 @@
+using System.Diagnostics;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace TaxBaik.Admin.Pages;
+
+[ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
+[IgnoreAntiforgeryToken]
+public class ErrorModel : PageModel
+{
+    public string? RequestId { get; set; }
+
+    public bool ShowRequestId => !string.IsNullOrEmpty(RequestId);
+
+    private readonly ILogger<ErrorModel> _logger;
+
+    public ErrorModel(ILogger<ErrorModel> logger)
+    {
+        _logger = logger;
+    }
+
+    public void OnGet()
+    {
+        RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier;
+    }
+}