CmdPal: Make IconBox unfocusable and unreachable by keyboard navigation by default (#40636)

## Summary of the Pull Request
IconBox controls no longer receive keyboard focus by default. as their
focus state is not visually represented and they serve primarily as
decorative roles in the application. For cases where keyboard navigation
on an IconBox is desired, focusability can be enabled explicitly on the
specific instance.

<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist

- [x] **Closes:** #40617
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/Microsoft.CmdPal.UI/Controls/IconBox.cs

@@ -7,6 +7,8 @@ using Microsoft.CmdPal.UI.Deferred;
 using Microsoft.UI.Dispatching;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Input;
+
 using Windows.Foundation;
 
 namespace Microsoft.CmdPal.UI.Controls;
@@ -49,6 +51,12 @@ public partial class IconBox : ContentControl
     /// </summary>
     public event TypedEventHandler<IconBox, SourceRequestedEventArgs>? SourceRequested;
 
+    public IconBox()
+    {
+        TabFocusNavigation = KeyboardNavigationMode.Once;
+        IsTabStop = false;
+    }
+
     private static void OnSourcePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
     {
         if (d is IconBox @this)