Address Copilot review feedback: fix misleading links, stale UWP heading, missing C++ include

- best-practices.md: fix 'Distribute through Store' link from MSIX source-code-overview to actual Store distribution article
- packaging/index.md: fix Store scenario table row link to Store distribution article
- modernize-packaged-apps.md: rename 'Extend with UWP components' section to 'Use the Windows App SDK in an existing project' with updated body; fix distribute link to package-and-deploy overview
- toc.yml: rename TOC node to match modernized section heading
- desktop-to-uwp-enhance.md: add missing <string> and <string_view> includes for C++ wstring_view snippet

Co-authored-by: Copilot <[email protected]>

Author: GrantMeStrength

hub/apps/desktop/modernize/modernize-packaged-apps.md

@@ -32,9 +32,9 @@ Starting in Windows 10, version 1809, packaged apps can retrieve certain kinds o
 
 For more info, see [Get activation info for packaged apps](get-activation-info-for-packaged-apps.md).
 
-## Extend with UWP components
+## Use the Windows App SDK in an existing project
 
-Some Windows experiences (for example, a touch-enabled UI page) must run inside of an AppContainer. In general, you should first determine whether you can add your experience by [enhancing](desktop-to-uwp-enhance.md) your existing desktop app with Windows Runtime APIs. If you have to use a UWP component to achieve the experience, then you can add a UWP project to your solution, and use app services to communicate between your desktop app and the UWP component.
+You can use the Windows App SDK to add modern Windows features—such as WinUI 3 controls, push notifications, and app lifecycle management—to your existing Win32 or .NET desktop app without requiring a full rewrite.
 
 For more information, see [Add Windows App SDK features to your existing project](/windows/apps/windows-app-sdk/use-windows-app-sdk-in-existing-project).