fix: resolve AfterBlazorClientSide build error from UI overhaul

The UI overhaul added ComponentCatalog-driven NavMenu and SearchBox
components to AfterBlazorServerSide. Since AfterBlazorClientSide links
Layout files via content references, it needs:

- ComponentCatalog.cs linked as a compile item (NavMenu depends on it)
- @using AfterBlazorServerSide added to client _Imports.razor
- @using AfterBlazorServerSide.Components.Shared moved from
  MainLayout.razor to server-side _Imports.razor (avoids namespace
  resolution failure in client project where Shared components are
  not linked)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: csharpfritz

samples/AfterBlazorClientSide/AfterBlazorClientSide.csproj

@@ -15,6 +15,7 @@
     <Content Include="..\AfterBlazorServerSide\Components\Layout\**">
       <Link>Layout\%(RecursiveDir)%(Filename)%(Extension)</Link>
     </Content>
+    <Compile Include="..\AfterBlazorServerSide\ComponentCatalog.cs" Link="ComponentCatalog.cs" />
     <Content Include="..\AfterBlazorServerSide\Ads.xml" Link="wwwroot\Ads.xml">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>

samples/AfterBlazorClientSide/_Imports.razor

@@ -6,5 +6,6 @@
 @using Microsoft.JSInterop
 @using AfterBlazorClientSide
 @using AfterBlazorClientSide.Layout
+@using AfterBlazorServerSide
 @using BlazorWebFormsComponents
 @using SharedSampleObjects.Models

samples/AfterBlazorServerSide/Components/Layout/MainLayout.razor

@@ -1,5 +1,4 @@
 @inherits LayoutComponentBase
-@using AfterBlazorServerSide.Components.Shared
 
 <div class="layout-wrapper" data-bs-theme="light">
     <!-- Top Navbar -->

samples/AfterBlazorServerSide/_Imports.razor

@@ -9,4 +9,5 @@
 @using AfterBlazorServerSide
 @using AfterBlazorServerSide.Components
 @using AfterBlazorServerSide.Components.Layout
+@using AfterBlazorServerSide.Components.Shared
 @using static Microsoft.AspNetCore.Components.Web.RenderMode