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/App.razor

@@ -0,0 +1,12 @@
+<Router AppAssembly="@typeof(App).Assembly">
+    <Found Context="routeData">
+        <RouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)" />
+        <FocusOnNavigate RouteData="@routeData" Selector="h1" />
+    </Found>
+    <NotFound>
+        <PageTitle>Not found</PageTitle>
+        <LayoutView Layout="@typeof(MainLayout)">
+            <p role="alert">Sorry, there's nothing at this address.</p>
+        </LayoutView>
+    </NotFound>
+</Router>