CmdPal: Add a button to toggle the visibility of the dev ribbon (#45379)

## Summary of the Pull Request

This PR adds an option to toggle visibility of the dev ribbon. The state
is only temporary and does not persist across app runs -- that is
intentional to prevent the dev from turning it off permanently.

<img width="648" height="519" alt="image"
src="https://github.com/user-attachments/assets/c5b348f6-8f3c-4ec2-a250-e051fd003e09"
/>

<img width="1313" height="751" alt="image"
src="https://github.com/user-attachments/assets/89928e30-b0dc-4a14-b5fb-bf68357a145b"
/>


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## PR Checklist

- [x] Closes: #45371
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **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

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/Microsoft.CmdPal.UI/MainWindow.xaml.cs

@@ -54,6 +54,7 @@ public sealed partial class MainWindow : WindowEx,
     IRecipient<ErrorOccurredMessage>,
     IRecipient<DragStartedMessage>,
     IRecipient<DragCompletedMessage>,
+    IRecipient<ToggleDevRibbonMessage>,
     IDisposable,
     IHostWindow
 {
@@ -91,6 +92,8 @@ public sealed partial class MainWindow : WindowEx,
 
     private bool _preventHideWhenDeactivated;
 
+    private DevRibbon? _devRibbon;
+
     private MainWindowViewModel ViewModel { get; }
 
     public bool IsVisibleToUser { get; private set; } = true;
@@ -139,6 +142,7 @@ public sealed partial class MainWindow : WindowEx,
         WeakReferenceMessenger.Default.Register<ErrorOccurredMessage>(this);
         WeakReferenceMessenger.Default.Register<DragStartedMessage>(this);
         WeakReferenceMessenger.Default.Register<DragCompletedMessage>(this);
+        WeakReferenceMessenger.Default.Register<ToggleDevRibbonMessage>(this);
 
         // Hide our titlebar.
         // We need to both ExtendsContentIntoTitleBar, then set the height to Collapsed
@@ -212,7 +216,8 @@ public sealed partial class MainWindow : WindowEx,
         // Add dev ribbon if enabled
         if (!BuildInfo.IsCiBuild)
         {
-            RootElement.Children.Add(new DevRibbon { Margin = new Thickness(-1, -1, 120, -1) });
+            _devRibbon = new DevRibbon { Margin = new Thickness(-1, -1, 120, -1) };
+            RootElement.Children.Add(_devRibbon);
         }
     }
 
@@ -1134,6 +1139,11 @@ public sealed partial class MainWindow : WindowEx,
         DisposeAcrylic();
     }
 
+    public void Receive(ToggleDevRibbonMessage message)
+    {
+        _devRibbon?.Visibility = _devRibbon.Visibility == Visibility.Visible ? Visibility.Collapsed : Visibility.Visible;
+    }
+
     public void Receive(DragStartedMessage message)
     {
         _preventHideWhenDeactivated = true;